JP2007315321A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the worsening of exhaust gas properties due to the fact that fuel residing in a combustion chamber or in an intake passage is exhausted as unburnt gas in starting an engine. <P>SOLUTION: The engine 10 has a plurality of cylinders 12a-12d (12a only shown in Fig.1), and a valve drive mechanism 20 for opening/closing exhaust valves 19 and intake valves 18 provided in the cylinders 12a-12d. An ECU 90 for controlling the intake valves 18 and the exhaust valves 19 to be opened/closed by the valve drive mechanism 20 executes valve holding control to hold all exhaust valves 19 in fully closing conditions while holding the intake valves 18 in valve opening conditions during cranking the engine 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to an internal combustion engine having a drive mechanism that opens and closes an exhaust valve and an intake valve, and a control device that controls opening and closing of each valve by the drive mechanism.

A cylinder injection type internal combustion engine in which fuel is directly injected into a cylinder from a fuel injection valve has been put into practical use.
In such an in-cylinder internal combustion engine, the tip of the fuel injection valve is exposed in the combustion chamber, and the fuel injection valve is exposed to the high temperature and high pressure in the cylinder. Therefore, the fuel seal portion of the fuel injection valve is likely to deteriorate. In addition, there may be a seal failure due to the inclusion of foreign matter between the valve body that opens and closes the injection port and the wear of the contact portion between the injection port and the valve body. There is a risk of fuel leaking into the cylinder.

As described above, if the fuel remains in the cylinder when the engine is stopped, the air-fuel ratio in the cylinder at the next engine start becomes excessively rich by the amount of the remaining fuel vaporized. The nature will decline. Therefore, in the apparatus described in Patent Document 1, the exhaust valve is kept open when the engine is started, and the residual fuel in the cylinder is scavenged.
JP 2000-64861 A

By the way, if the exhaust valve is kept open when the engine is started, the following inconvenience occurs.
That is, the fuel remaining in the cylinder when the engine is stopped is discharged to the exhaust passage without being burned until the first explosion occurs at the time of starting the engine. Therefore, in the initial stage of engine startup (between the start of cranking and the first explosion), unburned gas containing a large amount of hydrocarbons (hereinafter referred to as HC) is exhausted, and exhaust at the time of engine startup is exhausted. The properties will deteriorate. The occurrence of such inconvenience cannot be ignored in terms of improving exhaust purification performance, which is a strong requirement for internal combustion engines in recent years.

  The above-described deterioration of exhaust properties due to the fuel remaining in the cylinder occurs not only in the cylinder injection type internal combustion engine but also in the intake port injection type internal combustion engine in which the fuel is injected into the intake port. There is a fear. That is, in such an intake port injection type internal combustion engine, fuel adheres and remains in the intake passage, and therefore, until the first explosion occurs at the start of the engine, the adhering fuel, that is, the vaporized fuel resulting from the residual fuel is not. There is a possibility that exhaust gas will be discharged to the exhaust passage without being burned and the exhaust properties will deteriorate.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress the deterioration of exhaust properties due to the fuel remaining in the cylinder or the intake passage being discharged as unburned gas when the engine is started. An object of the present invention is to provide a control device for an internal combustion engine.

Hereinafter, means for solving the above-described object and its operation and effects will be described.
The invention according to claim 1 is an internal combustion engine comprising a plurality of cylinders and a drive mechanism that opens and closes an exhaust valve and an intake valve provided in each cylinder, and controls the opening and closing of each valve by the drive mechanism. The gist of the control device is to perform valve holding control for holding all of the exhaust valves in a fully closed state and holding the intake valves in an open state during cranking of the internal combustion engine.

  According to this configuration, since all the exhaust valves are kept closed during cranking at the time of engine start, release of unburned gas from the exhaust passage into the atmosphere is suppressed at the time of engine start. Further, since the intake valve is held open during cranking at the time of engine start, when the piston rises in one of the plurality of cylinders, unburned gas together with air in the cylinder is taken into the intake passage. To be discharged. And since the unburned gas discharged | emitted by this intake passage is suck | inhaled by the other cylinder from which a piston descend | falls, discharge | release of unburned gas from the intake passage to air | atmosphere is also suppressed. Therefore, according to this configuration, it is possible to suppress the deterioration of the exhaust property due to the fuel remaining in the cylinder or the intake passage being discharged as unburned gas when the engine is started.

  Further, according to the second or third aspect of the invention, in the execution of the valve holding control, all the intake valves of each cylinder are held in the open state, or the intake valves are held in the fully open state. By adopting such a configuration, it is possible to reduce the pressure loss at the time of intake and exhaust of air in each cylinder that is executing the valve holding control. Therefore, for example, it is possible to reduce the rotational load of the crankshaft during cranking.

  According to a fourth aspect of the present invention, in the control device for an internal combustion engine according to any one of the first to third aspects, an air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust, and an amount of fuel supplied to the cylinder are determined. A fuel amount adjusting means for adjusting the fuel injection amount at the next engine start based on the air-fuel ratio detected after the execution of the valve holding control is completed and the valve opening operation of the exhaust valve is started. The gist is to adjust.

  By executing the valve holding control, the unburned gas remains in the intake passage and the cylinder and is not discharged. Therefore, when the engine is started, the fuel is increased by the amount of the unburned gas, and torque fluctuation and exhaust Deterioration of properties may occur. Here, since the amount of unburned gas is reflected in the air-fuel ratio of the exhaust gas detected after the valve holding control is finished and the valve opening operation of the exhaust valve is started, the amount of unburned gas is reflected from the air-fuel ratio. The amount of gas can be estimated. Therefore, in the configuration described in claim 4, the fuel injection amount at the next engine start is calculated based on the air-fuel ratio detected after the execution of the valve holding control is finished and the exhaust valve opening operation is started. By adjusting the fuel injection amount at the next start in consideration of the amount of unburned gas, the air-fuel ratio at the next start approaches an ideal state. Therefore, it is possible to suitably suppress the torque fluctuation and the deterioration of the exhaust property at the time of starting the engine.

  In addition, since it can be estimated that the amount of unburned gas is larger as the richness of the air-fuel ratio is higher, when adjusting the fuel injection amount at the next engine start based on the air-fuel ratio, According to the fifth aspect of the invention, the fuel injection amount can be appropriately set by decreasing the fuel injection amount as the air-fuel ratio richness is higher.

  According to a sixth aspect of the present invention, in the control device for an internal combustion engine according to any one of the first to fifth aspects, the valve holding control is performed so that the engine rotational speed during cranking is equal to or higher than the initial explosion occurrence rotational speed. The gist is that it ends at some point.

  The unburned gas remaining in the intake passage and the cylinder can be processed in conjunction with the combustion of the air-fuel mixture after the first explosion. Here, the initial explosion at the start of the engine is likely to occur when the rotational speed of the crankshaft rotated by the starter motor increases to some extent. In view of this, the valve holding control may be executed until a preset time elapses after the engine start is started. In addition, as in the above configuration, the engine speed during cranking is initially set. The valve holding control may be terminated when the explosion generating rotational speed is exceeded. In this case, since the valve holding control is terminated when the engine state is likely to cause the first explosion, the period during which the unburned gas is discharged without being subjected to the combustion process can be shortened as much as possible. it can. Therefore, according to this configuration, the end timing of the valve holding control can be appropriately set while suppressing the deterioration of the exhaust property. The rotation speed at which the first explosion is likely to occur can be obtained through a prior experiment or the like.

  According to a seventh aspect of the present invention, in the control device for an internal combustion engine according to the sixth aspect, in addition to the condition that the engine rotational speed is equal to or higher than the initial explosion occurrence rotational speed, the valve holding control is performed for each cylinder. The exhaust valve and the intake valve of the cylinder in which the piston is in the upward stroke are closed with the end of the valve holding control. This is the gist.

  According to this configuration, when the piston in the cylinder reaches the upward stroke, the valve holding control is terminated and the exhaust valve and the intake valve of the cylinder are closed, so that the piston is in the upward stroke. The cylinder state quickly enters the compression stroke. For this reason, when the valve holding control is terminated when the engine speed during cranking exceeds the initial explosion generating rotational speed, the time until the first explosion occurs after the valve holding control is terminated. It can be made shorter. Therefore, it becomes possible to more reliably suppress the discharge of unburned gas.

  According to an eighth aspect of the present invention, in the control device for an internal combustion engine according to any one of the fourth to seventh aspects, an execution period of the valve holding control at the next engine start is set to the variation amount of the air-fuel ratio. The gist is to set based on this.

  The amount of unburned gas remaining in the cylinder, the intake passage, and the like may vary from cylinder to cylinder depending on the state of the fuel injection valve and the opening and closing states of the intake and exhaust valves when the engine is stopped. Therefore, even when the fuel injection amount is adjusted based on the air-fuel ratio as described above, if the variation in the amount of unburned gas between the cylinders is large, the air-fuel ratio becomes different for each cylinder. As a result, the air-fuel ratio may vary. Here, during execution of the valve holding control, unburned gas travels through each cylinder through the intake passage, so each cylinder communicated with this intake passage or in the intake passage communicated with each cylinder. The amount of unburned gas is made uniform. However, when the execution time of the valve holding control is short, such uniformization is not sufficiently performed, and there is a possibility that variation in the amount of unburned gas between the cylinders cannot be sufficiently suppressed. In that respect, as in the above configuration, the execution period of the valve holding control is set based on the fluctuation amount of the air-fuel ratio detected after the execution of the valve holding control is ended and the valve opening operation of the exhaust valve is started. By doing so, the execution period is set in consideration of variations in the amount of unburned gas between the cylinders, so that such variations can be suitably suppressed. Therefore, it is possible to appropriately suppress fluctuations in the air-fuel ratio when starting the engine.

  Note that it can be estimated that the variation in the amount of unburned gas increases as the amount of fluctuation in the air-fuel ratio increases, and therefore, when the execution period is set based on the amount of fluctuation in the air-fuel ratio, a claim is provided. As described in the seventh aspect of the invention, the execution period of the valve holding control can be appropriately set by increasing the execution period of the valve holding control as the variation amount of the air-fuel ratio is larger.

  A tenth aspect of the present invention is the control apparatus for an internal combustion engine according to any one of the first to ninth aspects, wherein the drive mechanism is configured to open and close the exhaust valve and the intake valve by electromagnetic force. That is the gist.

  According to this configuration, the exhaust valve and the intake valve are configured as so-called electromagnetically driven valves. Therefore, the timing of valve opening and closing of each cylinder can be freely controlled without synchronizing with the rotation of the crankshaft, and the above valve holding control can be easily realized.

  The invention according to claim 11 is the control apparatus for an internal combustion engine according to any one of claims 1 to 10, wherein the internal combustion engine is a direct injection internal combustion engine in which fuel is directly supplied into the cylinder. That is the gist.

  As described above, in a cylinder injection internal combustion engine, the tip of the fuel injection valve is exposed in the combustion chamber, and the fuel injection valve is exposed to the high temperature and high pressure in the cylinder. Therefore, the fuel seal part is likely to deteriorate. In addition, foreign matter may be trapped between the valve body that opens and closes the injection port and wear of the contact portion between the injection port and the valve body may cause a seal failure. There is a possibility of leakage. Therefore, in an in-cylinder injection type internal combustion engine, there is a possibility that the exhaust characteristics at the start of the engine are significantly deteriorated as compared with an intake port injection type internal combustion engine in which fuel is injected into the intake port. In this respect, according to the same configuration, in such an in-cylinder injection type internal combustion engine, it is possible to suppress the fuel remaining in the cylinder when the engine is stopped from being released into the atmosphere as unburned gas when cranking. it can.

  Hereinafter, the configuration of an internal combustion engine control apparatus according to the present invention applied to an internal combustion engine in which an intake valve and an exhaust valve are driven by electromagnetic force will be described with reference to FIGS. .

  First, a schematic configuration of the engine 10 to which the control device in this embodiment is applied will be described with reference to FIGS. 1 and 2. 1 is a schematic diagram illustrating a schematic configuration of the engine 10, and FIG. 2 is a schematic diagram illustrating configurations of an intake system and an exhaust system of the engine 10.

  As shown in FIGS. 1 and 2, the engine 10 includes a cylinder block 11 having a cylindrical first cylinder 12a, a second cylinder 12b, a third cylinder 12c, and a fourth cylinder 12d (the first cylinder in FIG. 1). This is an in-line four-cylinder engine having four cylinders. The cylinders 12a to 12d are formed in the order of the first cylinder 12a, the second cylinder 12b, the third cylinder 12c, and the fourth cylinder 12d in the longitudinal direction of the cylinder block 11. In addition, the cylinder 12 described below refers to each cylinder such as the first cylinder 12a to the fourth cylinder 12d.

  As shown in FIG. 1, a cylinder head 13 is assembled to the upper part of the cylinder block 11. The cylinder 12 is provided with a piston 14 that moves up and down on the inner surface thereof. The piston 14 is connected to the crankshaft 25 via a connecting rod 29. When the positions of the pistons 14 of the first cylinder 12a and the fourth cylinder 12d are both at the top dead center, the positions of the pistons 14 of the second cylinder 12b and the third cylinder 12c are both at the bottom dead center. Thus, the crankshaft 25 is formed. Thereby, the moving direction of each piston 14 of the second cylinder 12b and the third cylinder 12c is opposite to the moving direction of each piston 14 of the first cylinder 12a and the fourth cylinder 12d. That is, when the pistons 14 of the first cylinder 12a and the fourth cylinder 12d are both in the upward stroke, the pistons 14 of the second cylinder 12b and the third cylinder 12c are both in the downward stroke. Conversely, when the pistons 14 of the first cylinder 12a and the fourth cylinder 12d are both in the downward stroke, the pistons 14 of the second cylinder 12b and the third cylinder 12c are both in the upward stroke.

  A starter motor 80 is drivingly connected to the crankshaft 25. When the engine is started, the crankshaft 25 is rotated by the starter motor 80 to perform cranking. A disc-shaped timing rotor 100 is provided at the end of the crankshaft 25. A plurality of teeth are provided for each equiangular angle on the outer periphery of the timing rotor 100, and some teeth are missing. A crank angle sensor 51 is provided so as to face the teeth of the timing rotor 100. Each time the teeth of the timing rotor 100 pass in front of the crank angle sensor 51, a pulse signal is output from the crank angle sensor 51. Then, the crank angle sensor 51 detects the missing tooth portion of the timing rotor 100, thereby detecting the reference position of the crankshaft 25 (for example, the top dead center of a specific cylinder), and the crankshaft 25 based on the pulse signal. Is detected, that is, the crank angle CK. Further, the engine speed NE is calculated based on the changing speed of the crank angle CK.

Inside the cylinder 12, combustion chambers 15 defined by the wall surface of the cylinder 12, the upper surface of the piston 14 and the lower surface of the cylinder head 13 are formed.
In the cylinder head 13, a fuel injection valve 24 for directly injecting fuel into the combustion chamber 15 and a spark plug 23 for igniting the air-fuel mixture in the combustion chamber 15 correspond to the first cylinder 12a to the fourth cylinder 12d, respectively. The tip of the fuel injection valve 24 where the fuel injection hole is formed is exposed in the combustion chamber 15. Further, the cylinder head 13 is formed with an intake port 16 and an exhaust port 17 communicating with each combustion chamber 15. Two intake ports 16 and two exhaust ports 17 are formed for each combustion chamber 15.

  An intake valve 18 for opening and closing the intake port 16 is provided at the downstream opening end (opening end on the combustion chamber 15 side) of each intake port 16. The intake valve 18 is driven to open and close by a valve drive mechanism 20 described later. An intake manifold 31 is connected to the upstream opening end of each intake port 16, and the upstream opening end of the intake manifold 31 is connected to a surge tank 32 that smoothes the pulsation of intake air. Yes. An intake passage 30 is connected to the surge tank 32, and an air cleaner for removing dust in the intake air is provided at the upstream opening end of the intake passage 30. Further, a throttle valve 33 for adjusting the amount of intake air is provided between the air cleaner and the surge tank 32 in the intake passage 30. The opening degree of the throttle valve 33 is controlled by an electronic control unit 90 (hereinafter referred to as ECU 90) that performs various controls of the engine 10 in an integrated manner.

  Exhaust valves 19 for opening and closing the exhaust ports 17 are provided at the upstream open ends (open ends on the combustion chamber 15 side) of the exhaust ports 17, respectively. The exhaust valve 19 is also driven to open and close by a valve drive mechanism 20 described later. An exhaust manifold 41 is connected to each downstream opening end of each exhaust port 17, and a downstream side of this exhaust manifold 41 is connected to an exhaust passage 40. In the middle of the exhaust passage 40, a catalytic converter 42 including a three-way catalyst is provided. By the oxidation-reduction action of the catalytic converter 42, unburned components such as HC, nitrogen oxides, and carbon monoxide contained in the exhaust gas are purified.

  Fuel is injected from the fuel injection valve 24 into the intake air supplied to the combustion chamber 15 by opening the intake valve 18, and an air / fuel mixture is formed in the combustion chamber 15. The air-fuel mixture is burned by being ignited by the spark plug 23, and the piston 14 is pushed down by the combustion gas, whereby the crankshaft 25 is rotated. In this embodiment, the order of ignition of the air-fuel mixture is in the order of the first cylinder 12a, the third cylinder 12c, the fourth cylinder 12d, and the second cylinder 12b.

  The combusted air-fuel mixture, that is, exhaust gas, is discharged into the exhaust passage 40 when the exhaust valve 19 is opened. After being purified by the catalytic converter 42 provided in the exhaust passage 40, the exhaust gas is discharged to the outside of the exhaust passage 40.

Next, the configuration of the valve driving mechanism 20 that drives the intake valve 18 and the exhaust valve 19 will be described with reference to FIG.
The valve drive mechanism 20 that drives the intake valve 18 and the valve drive mechanism 20 that drives the exhaust valve 19 have the same basic configuration and drive control mode, and are different only in the valve to be driven. Therefore, in the following, the valve drive mechanism 20 of the exhaust valve 19 will be described as an example.

As shown in FIG. 3, the exhaust valve 19 includes a valve shaft 19a and an umbrella portion 19b provided at one end of the valve shaft 19a.
The valve drive mechanism 20 is disposed coaxially with the valve shaft 19a of the exhaust valve 19 supported so as to be reciprocally supported by the cylinder head 13, and reciprocally drives the armature shaft 226 and reciprocates together with the valve shaft 19a. By doing so, it includes an electromagnetic drive unit 221 that drives the exhaust valve 19 to reciprocate.

A valve seat 215 is formed on the peripheral edge of the opening end of the exhaust port 17. As the valve shaft 19a reciprocates, the umbrella portion 19b is separated from and seated on the valve seat 215, thereby opening and closing the exhaust port 17.
In the valve shaft 19a, a lower retainer 222 is fixed to the end opposite to the end where the umbrella portion 19b is provided. A lower spring 224 is disposed in a compressed state between the lower retainer 222 and the cylinder head 13. The exhaust valve 19 is biased in the valve closing direction (upward in FIG. 3) by the elastic force of the lower spring 224.

  A disk-shaped armature 228 made of a high magnetic permeability material is fixed to a substantially central portion in the axial direction of the armature shaft 226. One end of the armature shaft 226 is in contact with the end of the valve shaft 19a on the lower retainer 222 side. On the other hand, an applicator 230 is fixed to the other end of the armature shaft 226.

  In the casing (not shown) of the electromagnetic drive unit 221, the upper core 232 is positioned and fixed between the upper retainer 230 and the armature 228. Similarly, in this casing, a lower core 234 is positioned and fixed between the armature 228 and the lower retainer 222. Each of the upper core 232 and the lower core 234 is formed in a ring shape from a high magnetic permeability material, and an armature shaft 226 is inserted in a central portion thereof so as to be able to reciprocate.

  An upper spring 238 is disposed in a compressed state between the upper cap 236 and the upper retainer 230 provided in the casing. The exhaust valve 19 is biased in the valve opening direction (downward in FIG. 3) by the elastic force of the upper spring 238.

  A displacement amount sensor 54 for detecting the displacement state of the exhaust valve 19 is attached to the upper cap 236. The displacement sensor 54 outputs a voltage signal that changes in accordance with the distance between the displacement sensor 54 and the applicator 230. Therefore, the displacement amount of the armature shaft 226 and the valve shaft 19a, in other words, the lift position of the exhaust valve 19 can be detected based on this voltage signal.

  An annular groove 240 centering on the axis of the armature shaft 226 is formed on a surface of the upper core 232 facing the armature 228, and an annular upper coil 242 is disposed in the groove 240. The upper coil 242 and the upper core 232 constitute a closing drive electromagnet 261 for driving the exhaust valve 19 in the valve closing direction (upward in FIG. 3).

  On the other hand, an annular groove 244 centering on the axis of the armature shaft 226 is formed on the surface of the lower core 234 facing the armature 228, and an annular lower coil 246 is disposed in the groove 244. The lower coil 246 and the lower core 234 constitute an open driving electromagnet 262 for driving the exhaust valve 19 in the valve opening direction (downward in FIG. 3).

The coils 242 and 246 of the electromagnets 261 and 262 are energized and controlled by the ECU 90 that performs various controls of the internal combustion engine.
FIG. 3 shows the state of the exhaust valve 19 when no drive current is supplied to any of the electromagnets 261 and 262 and no electromagnetic force is generated in each of the electromagnets 261 and 262. In this state, the armature 228 is not attracted by the electromagnetic force of the electromagnets 261 and 262, and is stationary at an intermediate position between the cores 232 and 234 where the urging forces of the springs 224 and 238 are balanced. . In this state, the umbrella portion 19b is separated from the valve seat 215, and the exhaust valve 19 is in a half-open state. Hereinafter, the position of the exhaust valve 19 in this state is referred to as a neutral position.

  Next, a mode when the exhaust valve 19 is displaced from one displacement end toward the other displacement end, that is, an operation mode of the exhaust valve 19 that is driven to open and close through energization control with respect to the electromagnets 261 and 262 will be described.

  When the exhaust valve 19 is closed, a holding current for holding the exhaust valve 19 in the fully closed state is supplied to the closing drive electromagnet 261. By supplying this holding current, the armature 228 is attracted by the electromagnetic force of the closing drive electromagnet 261, abuts against the upper core 232 against the elastic force of the upper spring 238, and the umbrella portion 19 b contacts the valve seat 215. The seated state is maintained.

  Next, when the opening timing of the exhaust valve 19 arrives, the electromagnetic force of the closing drive electromagnet 261 is reduced from that time until the exhaust valve 19 reaches a position on the valve closing side by a predetermined amount from the neutral position. Energization control is performed. During this period, the armature 228 is separated from the upper core 232 and the exhaust valve 19 is displaced in the valve opening direction, and the displacement driving magnet is not excessively increased by an external force based on the in-cylinder pressure or the exhaust pressure. The electromagnetic force that attracts the armature 228 is controlled through adjustment of the driving current for the H.261.

  When the exhaust valve 19 is displaced by a predetermined amount from the fully closed position, the closed drive electromagnet 261 and the open drive electromagnet 261 are opened for a period until the exhaust valve 19 reaches a position on the valve opening side by a predetermined amount from the neutral position. Any supply of drive current to the electromagnet 262 is stopped.

  Thereafter, when the exhaust valve 19 is further displaced by the elastic force of the upper spring 238 and reaches a position on the valve opening side by a predetermined amount from the neutral position, the exhaust valve 19 is opened for a period from that time until the exhaust valve 19 reaches the fully open position. Energization control for the drive electromagnet 262 is performed. During this period, the electromagnetic force that attracts the exhaust valve 19 in the valve opening direction is controlled through adjustment of the drive current to the electromagnet 262 for driving to ensure that the exhaust valve 19 reaches the fully opened position with a predetermined displacement speed.

  When the exhaust valve 19 reaches the fully open position, a holding current for holding the exhaust valve 19 in the fully open state is supplied to the open driving electromagnet 262. By supplying this holding current, the armature 228 is attracted by the electromagnetic force of the opening driving electromagnet 262 and abuts against the lower core 234 against the elastic force of the lower spring 224, and the umbrella portion 19 b is separated from the valve seat 215. It is held in the most separated state.

  Next, when the exhaust drive timing of the exhaust valve 19 comes, the electromagnetic force of the open drive electromagnet 262 is reduced from that time until the exhaust valve 19 reaches a position on the valve opening side by a predetermined amount from the neutral position. Energization control is performed. During this period, the armature 228 is separated from the lower core 234 and the exhaust valve 19 is displaced in the valve closing direction, and the opening driving electromagnet is prevented so that the displacement speed at that time is not excessive due to the external force based on the in-cylinder pressure or the exhaust pressure. The electromagnetic force that attracts the exhaust valve 19 in the valve opening direction is controlled through the adjustment of the drive current for the H.262.

  Then, when the exhaust valve 19 is displaced by a predetermined amount from the fully open position, the closed drive electromagnet 261 and the open drive electromagnet from that time until the exhaust valve 19 reaches a position on the valve closing side by a predetermined amount from the neutral position. Any supply of drive current to 262 is stopped.

  Thereafter, when the exhaust valve 19 is further displaced by the elastic force or the like of the lower spring 224 and reaches a position on the valve closing side by a predetermined amount from the neutral position, the period from that time until the exhaust valve 19 reaches the fully closed position, Energization control for the closing drive electromagnet 261 is performed. During this period, the electromagnetic force that attracts the exhaust valve 19 in the valve closing direction is controlled through the adjustment of the drive current to the closing drive electromagnet 261 so that the exhaust valve 19 reliably reaches the fully closed position with a predetermined displacement speed. .

  When the exhaust valve 19 reaches the fully closed position, a holding current for holding the exhaust valve 19 in the fully closed state is applied to the closing drive electromagnet 261 from that time until the next opening drive timing comes. Will be supplied again.

The exhaust valve 19 and the intake valve 18 are driven to open and close through energization control to the valve drive mechanism 20.
As shown in FIG. 1, in addition to the crank angle sensor 51 and the displacement sensor 54, the engine 10 is provided with various sensors and switches for detecting the engine operating state. For example, an air flow meter 52 for detecting the intake air amount is provided in the intake passage 30 and upstream of the throttle valve 33, and the oxygen concentration in the exhaust is in the exhaust passage 40 and upstream of the catalytic converter 42. An air-fuel ratio sensor 53 is provided that can provide an output proportional to the. In addition, the cooling system of the engine 10 is provided with a water temperature sensor 55 that detects the temperature of the engine cooling water. Further, an engine start request by the driver is detected by an ignition switch 56 (hereinafter referred to as IG switch 56).

  The ECU 90 executes control programs and arithmetic processing based on the output signals of these various sensors and switches, and in each part of the apparatus such as the ignition plug 23, the fuel injection valve 24, the throttle valve 33, the valve drive mechanism 20, and the starter motor 80. Output a control signal.

  Incidentally, the tip of the fuel injection valve 24 of the engine 10 is exposed in the combustion chamber 15, and the fuel injection valve 24 is exposed to the high temperature and high pressure in the cylinder. Therefore, the fuel seal part of the fuel injection valve 24 is likely to deteriorate. In addition, there may be a seal failure due to the inclusion of foreign matter between the valve body that opens and closes the injection port and the wear of the contact portion between the injection port and the valve body. There is a risk of fuel leaking into the cylinder 12.

  Thus, the fuel remaining in the cylinder 12 when the engine is stopped is discharged into the exhaust passage 40 without being burned during cranking when the engine is started. For this reason, unburned gas containing a large amount of HC is discharged from the start of cranking to the initial explosion of the air-fuel mixture, and the exhaust properties at the start of the engine deteriorate.

  Therefore, in this embodiment, the intake valve 18 is opened during cranking at the start of the engine in order to suppress the deterioration of exhaust properties due to the fuel remaining in the cylinder 12 being discharged as unburned gas at the start of the engine. In addition, the valve holding control for holding the exhaust valve 19 in the closed state is executed.

Hereinafter, with reference to FIGS. 4 to 6, the control at the time of engine start of the engine 10 will be described.
FIG. 4 shows a control processing procedure when the engine 10 is started. This process is executed by the ECU 90 when the IG switch 56 is turned from “OFF” to “ON” by the driver.

  When this process is started, in step S100, a control signal is output to the valve drive mechanism 20, and all the intake valves 18 are held open, and all the exhaust valves 19 are held closed. Valve holding control is started. When this valve holding control is started, energization is performed to the open driving electromagnet 262 of the electromagnetic drive unit 221 that drives the intake valve 18, and the intake valve 18 is held in a fully open state. Further, energization is performed to the closing drive electromagnet 261 of the electromagnetic drive unit 221 that drives the exhaust valve 19, and the exhaust valve 19 is held in a fully closed state.

  When it is detected that all the intake valves 18 are fully opened and all the exhaust valves 19 are fully closed based on the output signal of the displacement sensor 54, the starter is started in the next step S110. The motor 80 is driven and cranking is started. At this time, output of control signals to the spark plug 23 and the fuel injection valve 24 is prohibited. That is, in the initial stage of cranking, both fuel injection and ignition of the air-fuel mixture are prohibited.

  When the valve holding control is started, all the exhaust valves 19 are held in the closed state during cranking at the time of starting the engine. Therefore, at the time of starting the engine, unburned gas from the exhaust passage 40 to the atmosphere is discharged. Release is suppressed. Further, since all the intake valves 18 are kept open during cranking at the time of engine start, when the piston 14 in each cylinder 12 rises, unburned gas together with the air in that cylinder is taken into the intake manifold. 31 is discharged. The unburned gas discharged to the intake manifold 31 is sucked into the other cylinders where the piston 14 descends via the surge tank 32 and the intake manifold 31, and therefore unburned gas from the intake passage 30 to the atmosphere. The release of gas is also suppressed.

  When cranking is started in step S110, counting of the count value C is started in step S120. The count value C is a value obtained by counting the pulse signals output from the crank angle sensor 51 after cranking starts, and is synchronized with the rotation of the crankshaft 25, more specifically, with the change of the crank angle CK. The number of the vertical movements of the piston 14 in the cylinder 12 is reflected.

  Next, the routine proceeds to step S130, where it is determined whether or not the engine rotational speed NE is equal to or higher than the reference rotational speed NEst. The reference rotational speed NEst is set to the engine rotational speed at which the initial explosion is likely to occur by performing fuel injection and ignition of the air-fuel mixture after cranking is started. The optimum value is obtained through experiments and the like.

  If it is determined in step S130 that the engine rotational speed NE is less than the reference rotational speed NEst (step S130: NO), the process of step S130 is performed until the engine rotational speed NE becomes equal to or higher than the reference rotational speed NEst. Repeated. Then, when the engine rotational speed NE becomes equal to or higher than the reference rotational speed NEst (step S130: YES), the process of step S140 is performed next.

  In step S140, it is determined whether or not the count value C is greater than or equal to the threshold value Cst. The threshold Cst is set to the following value. That is, when the valve holding control is started, unburned gas in each cylinder 12 passes between the cylinders via the intake manifold 31 and the surge tank 32. Therefore, as the number of rotations of the crankshaft 25 increases, that is, as the number of vertical movements of the piston 14 in each cylinder 12 increases, the amount of unburned gas between the cylinders becomes easier to be uniform, and the air-fuel ratio becomes stable. To come. Therefore, in the present embodiment, the number of up / down movements of the piston 14 to such an extent that the amount of unburned gas between the cylinders is sufficiently uniform is obtained through experiments and the like, and a count corresponding to the number of up / down movements is obtained. The value C is set as the threshold value Cst. Incidentally, whether or not the amount of unburned gas between the cylinders is sufficiently uniform may be determined based on the elapsed time since the start of valve holding control and cranking. In addition, the uniformity of the unburned gas is directly affected by the number of vertical movements of the piston 14. Therefore, by making such a determination based on the count value C, it is possible to more accurately determine whether the amount of unburned gas is equalized compared to the case where the determination is performed based on the elapsed time. It becomes possible. When the count value C is less than the threshold value Cst (step S140: NO), the process of step S140 is repeated until the count value C becomes equal to or greater than the threshold value Cst. If the count value C is equal to or greater than the threshold value Cst (step S140: YES), the process of step S150 is performed next.

  In step S150, the current crank angle CK is read, and, of the first cylinder 12a and the second cylinder 12b, the cylinder in which the piston 14 is in the downward stroke (hereinafter referred to as an ignition preparation cylinder) is based on the crank angle CK. Detected.

  When the ignition preparation cylinder is detected, in the next step S160, fuel injection control and ignition control for starting fuel injection and ignition in synchronization with the crank angle CK are started for the ignition preparation cylinder.

  In the next step S170, when the piston 14 of the ignition preparation cylinder is changed from the downward stroke to the upward stroke, the valve holding control for the ignition preparation cylinder is ended. Simultaneously with the end of the valve holding control, the opening / closing control of the intake valve 18 and the exhaust valve 19 is controlled in accordance with the control of opening / closing in synchronization with the rotation of the crankshaft 25, that is, intake, compression, combustion, exhaust. It is switched to normal opening / closing control to be opened / closed. When the normal opening / closing control is started in step S170, both the intake valve 18 and the exhaust valve 19 are fully closed so that the state of the ignition preparation cylinder that has shifted to the upward stroke becomes the compression stroke. For the ignition ready cylinder that has been put into the compression stroke state, fuel injection is performed in the latter half of the compression stroke, and the mixture is ignited when the piston 14 reaches the vicinity of the top dead center. The air-fuel mixture in the ignition preparation cylinder is burned.

  When the valve holding control of the ignition preparation cylinder detected in step S150 is completed and the opening / closing of the intake valve 18 and the exhaust valve 19 is switched to the normal opening / closing control, in the next step S180, the normal operation for the remaining cylinders is performed. Control is sequentially started in accordance with the ignition sequence. Here, fuel injection control and ignition control for the remaining cylinders are started in the same manner as described above, and the end of valve holding control and normal opening / closing control are started (S180). For example, when the ignition preparation cylinder detected in step S150 is the first cylinder 12a, fuel injection is performed in the order of the third cylinder 12c, the fourth cylinder 12d, and the second cylinder 12b in the order described above. The control and the ignition control are started, and the end of the valve holding control and the normal opening / closing control are started.

  In the next step S190, whether all the cylinders 12 have been switched to the normal control, that is, whether fuel injection control and ignition control have been started, and control of the intake valve 18 and exhaust valve 19 has been switched to normal opening / closing control. Is determined. If it is determined in step S190 that all the cylinders 12 have not been switched to normal control (step S190: NO), the processes in steps S180 and S190 are performed until all the cylinders 12 are switched to normal control. Repeated.

  On the other hand, if it is determined in step S190 that all the cylinders 12 have been switched to normal control (step S190: YES), in the next step S200, the drive of the starter motor 80 is terminated and the engine is started. Completed. Then, this process ends.

  On the other hand, when such valve holding control is executed, unburned gas remains in the intake passage 30 and the cylinder 12 and is not discharged. Therefore, at the time of starting the engine, more specifically, at the time of the first explosion, the air-fuel mixture is combusted in a state where unburned gas is added to the fuel injected from the fuel injection valve 24. That is, when the engine is started, the amount of fuel is increased by the amount of such unburned gas, the air-fuel ratio becomes rich, and there is a possibility that torque fluctuation, exhaust property deterioration, etc. will occur.

Therefore, in this embodiment, the fuel injection amount at the next engine start is adjusted based on the air-fuel ratio after the first explosion reflecting the amount of unburned gas remaining in the cylinder 12.
Hereinafter, a processing procedure for adjusting the fuel injection amount at the next engine start will be described with reference to FIG.

  The processing shown in FIG. 5 is executed by the ECU 90 at the timing when the valve holding control is ended and the control of the intake valve 18 and the exhaust valve 19 is switched to the normal opening / closing control.

  First, in step S300, the air-fuel ratio of exhaust when the exhaust valve 19 is opened for the first time after the first explosion occurs, that is, the initial air-fuel ratio A / Fprim which is the air-fuel ratio of exhaust immediately after the first explosion is detected. In the next step S310, a correction value Qcorr for correcting the decrease in the fuel injection amount is calculated based on the initial air-fuel ratio A / Fprim. The calculation of the correction value Qcorr is performed with reference to a map as shown in FIG. As shown in FIG. 6, as the initial air-fuel ratio A / Fprim is smaller than the target air-fuel ratio A / Ftrg suitable for engine starting, that is, the richness of the initial air-fuel ratio A / Fprim is higher, It can be estimated that the amount of unburned gas is large. Therefore, the correction value Qcorr is set to increase as the initial air-fuel ratio A / Fprim decreases. Incidentally, when the initial air-fuel ratio A / Fprim is larger than the target air-fuel ratio A / Ftrg, the correction value Qcorr is set to “0”. As a result, the correction value Qcorr is set to a larger value as the richness of the air-fuel mixture containing unburned gas is higher in the cylinder where the first explosion has occurred.

  In the next step S330, the value stored in the backup memory of the ECU 90, which is the correction value Qcorr calculated at the previous engine start, is updated to the correction value Qcorr calculated this time. Processing is terminated.

  Then, based on the correction value Qcorr updated in this way, the fuel injection amount at the next engine start is adjusted. More specifically, at the time of the next engine start, when the fuel injection control is started in the previous step S160 and fuel injection is performed to the ignition preparation cylinder, it is set based on the temperature of the engine cooling water or the like. The correction value Qcorr updated at the previous engine start is reflected on the basic fuel injection amount Qbase. As a result, the basic fuel injection amount Qbase is corrected to decrease by an amount corresponding to the unburned gas in the cylinder 12, and the enrichment of the air-fuel ratio is suppressed.

Next, with reference to FIGS. 7 and 8, the operation of the process at the time of starting (the process shown in FIG. 4) will be described.
FIG. 7 shows a timing chart of the change in the engine rotational speed NE at the time of starting the engine and the switching timing of the valve control mode.

  At time T1, when the IG switch 56 is turned "ON" by the driver, valve holding control is started and cranking by the starter motor 80 is started. As a result, the engine rotational speed NE starts to increase. In addition, the count process of the count value C is started in accordance with the start of cranking.

  When the engine rotational speed NE becomes equal to or higher than the reference rotational speed NEst at time T2, it is determined whether or not the count value C is equal to or higher than the threshold value Cst. The holding control is continued (time T2 to time T3). When it is determined at time T3 that the count value C is equal to or greater than the threshold value Cst, the ignition preparation cylinder is continuously detected, and normal control for the ignition preparation cylinder is started. That is, the fuel injection control and the ignition control for the ignition preparation cylinder are started, and the valve control of the ignition preparation cylinder is switched from the valve holding control to the normal opening / closing control. Thereafter, normal control is sequentially started for the remaining cylinders, whereby initial explosions are sequentially generated in the cylinders 12 and the engine start is completed.

  In this way, the intake valve 18 is kept fully open and the exhaust valve 19 is fully closed over the period until the engine rotational speed NE becomes equal to or higher than the reference rotational speed NEst and the count value C becomes equal to or higher than the threshold value Cst. The held valve holding control is executed.

  FIG. 8 shows a timing chart of a change mode of the upward stroke and the downward stroke of the piston 14 and an example of switching timing of the valve control mode in each of the cylinders 12a to 12d. Hereinafter, the switching process of the valve control mode before and after time T3 in FIG. 7 will be described in detail with reference to FIG.

  While the valve holding control is executed for all the cylinders 12 (before time t5), the piston 14 moves up and down while the intake valve 18 is held in the fully open state and the exhaust valve 19 is held in the fully closed state. In the cylinder in which the piston 14 is in the downward stroke, air is sucked into the cylinder 12 from the intake passage 30. Further, in the cylinder in which the piston 14 is in the upward stroke, unburned gas in the cylinder 12 is discharged to the intake passage 30 and the like. As described above, during the valve holding control, the unburned gas in each cylinder 12 moves between the cylinders. For example, the unburned gas discharged from the first cylinder 12a and the fourth cylinder 12d to the surge tank 32 at the time t2 to the time t3 is the second cylinder 12b and the second cylinder 12b as shown by the solid line arrows in FIG. It is sucked into the three cylinders 12c. Further, from time t3 to time t4, the unburned gas discharged from the second cylinder 12b and the third cylinder 12c to the surge tank 32 is, as shown by the dotted arrows in FIG. It is sucked into the fourth cylinder 12d.

  When the engine rotational speed NE becomes equal to or higher than the reference rotational speed NEst and then the count value C reaches the threshold value Cst (time T3), the piston 14 is in the downward stroke of the first cylinder 12a and the second cylinder 12b. Detection of the cylinder, that is, the ignition preparation cylinder is performed. In this example, at time T3, the second cylinder 12b is detected as an ignition preparation cylinder, and fuel injection control and ignition control for the second cylinder 12b are started. Then, when the moving direction of the piston 14 of the second cylinder 12b changes from descending to rising (time t5), the valve holding control for the second cylinder 12b is finished, and the control of the intake valve 18 and the exhaust valve 19 is performed. It can be switched to normal opening / closing control. More specifically, at time t5, the intake valve 18 and the exhaust valve 19 are fully closed so that the state of the second cylinder 12b is in the compression stroke. Then, fuel injection is performed in the latter half of the compression stroke, and thereafter, the air-fuel mixture is ignited, whereby the air-fuel mixture in the second cylinder 12b is combusted. In the combustion stroke from time t6 to time t7, the second cylinder The unburned gas remaining in 12b is burned. Then, in the exhaust stroke from time t7 to time t8, the exhaust valve 19 of the second cylinder 12b is opened for the first time, and the exhaust is discharged to the exhaust passage 40.

  As described above, when the fuel injection control, the ignition control, and the valve control for the second cylinder 12b are shifted to the normal control, the shift to the normal control in the other cylinders is performed in the same manner. The cylinder 12c and the fourth cylinder 12d are performed in this order.

  For example, in the first cylinder 12a, fuel injection control and ignition control are started when the piston 14 is in the downward stroke between time t5 and time t6. Then, when the moving direction of the piston 14 changes from descending to ascending (time t6), the valve holding control is terminated and normal opening / closing control is started. Here, in order to set the state of the first cylinder 12a to the compression stroke, the intake valve 18 and the exhaust valve 19 are fully closed. Then, fuel injection is performed in the latter half of the compression stroke, and then the mixture is ignited, whereby the mixture in the first cylinder 12a is combusted. In the combustion stroke from time t7 to time t8, the first cylinder The unburned gas remaining in 12a is burned. In the exhaust stroke from time t8 to time t9, the exhaust valve 19 of the first cylinder 12a is opened for the first time, and the exhaust is discharged to the exhaust passage 40.

  Further, in the third cylinder 12c, fuel injection control and ignition control are started when the piston 14 is in the downward stroke between time t6 and time t7. Then, when the moving direction of the piston 14 changes from descending to ascending (time t7), the valve holding control is terminated and normal opening / closing control is started. Here, in order to set the state of the third cylinder 12c to the compression stroke, the intake valve 18 and the exhaust valve 19 are fully closed. Then, fuel injection is performed in the latter half of the compression stroke, and thereafter, the air-fuel mixture is ignited, whereby the air-fuel mixture in the third cylinder 12c is combusted. In the combustion stroke from time t8 to time t9, the third cylinder The unburned gas remaining in 12c is burned. In the exhaust stroke from time t9 to time t10, the exhaust valve 19 of the third cylinder 12c is opened for the first time, and the exhaust is discharged to the exhaust passage 40.

  In the fourth cylinder 12d, fuel injection control and ignition control are started when the piston 14 is in the downward stroke between time t7 and time t8. Then, when the moving direction of the piston 14 changes from descending to ascending (time t8), the valve holding control is terminated and normal opening / closing control is started. Here, in order to set the state of the fourth cylinder 12d to the compression stroke, the intake valve 18 and the exhaust valve 19 are fully closed. Then, fuel injection is performed in the latter half of the compression stroke, and thereafter, the air-fuel mixture is ignited, whereby the air-fuel mixture in the fourth cylinder 12d is combusted. In the combustion stroke from time t9 to time t10, the fourth cylinder The unburned gas remaining in 12d is burned. In the exhaust stroke from time t10 to time t11, the exhaust valve 19 of the fourth cylinder 12d is opened for the first time, and the exhaust is discharged to the exhaust passage 40.

According to this embodiment described above, the following effects can be obtained.
(1) Since all the exhaust valves 19 are kept closed during cranking when the engine is started, the release of unburned gas from the exhaust passage 40 to the atmosphere is suppressed when the engine is started. Further, since the intake valve 18 is kept open during cranking at the time of engine start, unburned gas in the cylinder from the cylinder in which the piston 14 of the cylinders 12a to 12d rises is surge tank 32. Etc. are discharged. And since the unburned gas discharged | emitted by this surge tank 32 etc. is suck | inhaled by the other cylinder from which piston 14 descend | falls, discharge | release of unburned gas from the intake passage 30 to air | atmosphere is also suppressed. Accordingly, it is possible to suppress the deterioration of the exhaust properties due to the fuel remaining in the cylinder 12 and the intake passage 30 being discharged as unburned gas when the engine is started.

  (2) Since all the intake valves 18 of each cylinder 12 are held in the fully open state, pressure loss can be reduced when air is sucked and discharged in each cylinder 12 during valve holding control. Therefore, the rotational load of the crankshaft 25 at the time of cranking can be reduced.

  (3) A correction value Qcorr is set based on the initial air-fuel ratio A / Fprim detected after the valve holding control is finished and the exhaust valve 19 is started to open, and the basics at the next engine start The fuel injection amount Qbase is corrected to decrease by the correction value Qcorr. Therefore, the basic fuel injection amount Qbase at the next start is adjusted in consideration of the amount of unburned gas, and the air-fuel ratio at the next start approaches an ideal state. Accordingly, it is possible to favorably suppress torque fluctuations and deterioration of exhaust properties when starting the engine.

  (4) The correction value Qcorr is set so as to increase as the initial air-fuel ratio A / Fprim decreases. Therefore, the basic fuel injection amount Qbase is further decreased as the richness of the initial air-fuel ratio A / Fprim is higher. Therefore, the fuel injection amount at the time of starting the engine can be appropriately set according to the amount of unburned gas in each cylinder 12.

  (5) The unburned gas remaining in the intake passage 30 and the cylinder 12 can be processed together with the combustion of the air-fuel mixture after the first explosion. Here, the initial explosion at the start of the engine is likely to occur when the rotational speed of the crankshaft 25 rotated by the starter motor 80 increases to some extent. Therefore, the valve holding control may be executed until a preset time elapses after the engine start is started. However, as in the above embodiment, the engine rotational speed NE during cranking is the first explosion. By making the generated rotational speed NEst or higher one of the conditions for ending the valve holding control, the following effects can be obtained. That is, since the valve holding control is ended when the engine state is in a state where the first explosion is likely to occur, the period during which the unburned gas is discharged without being subjected to the combustion process can be shortened as much as possible. Accordingly, it is possible to appropriately set the end timing of the valve holding control while suppressing the deterioration of the exhaust properties.

  (6) When the piston 14 in the cylinder 12 reaches the ascending stroke, the valve holding control is terminated and the exhaust valve 19 and the intake valve 18 of the cylinder are closed, so that the piston 14 enters the ascending stroke. The cylinder is in a compression stroke quickly. Therefore, when the valve holding control is terminated when the engine speed NE during cranking is equal to or higher than the reference rotational speed NEst, the time from the end of the valve holding control to the occurrence of the first explosion is set. It can be made shorter. Therefore, it becomes possible to more reliably suppress the discharge of unburned gas.

  (7) The exhaust valve 19 and the intake valve 18 are configured as so-called electromagnetically driven valves that are driven by a valve drive mechanism 20 using electromagnetic force. Therefore, the timing of valve opening and closing of each cylinder 12 can be freely controlled without synchronizing with the rotation of the crankshaft 25, and the above valve holding control can be easily realized.

  (8) In a cylinder injection internal combustion engine, the tip of the fuel injection valve is provided exposed in the combustion chamber, and the fuel injection valve is exposed to the high temperature and high pressure in the cylinder. Therefore, the fuel seal part is likely to deteriorate. In addition, foreign matter may be caught between the valve body that opens and closes the injection port and the contact between the injection port and the valve body may cause a seal failure. There is a possibility of leakage. Therefore, in an in-cylinder injection type internal combustion engine, there is a possibility that the exhaust characteristics at the start of the engine are significantly deteriorated as compared with an intake port injection type internal combustion engine in which fuel is injected into the intake port. In this regard, according to the above-described embodiment, in the in-cylinder injection engine 10, the fuel remaining in the cylinder 12 when the engine is stopped is prevented from being released into the atmosphere as unburned gas when cranking. be able to.

In addition, the said embodiment can also be implemented with the following forms which changed this suitably.
The amount of unburned gas remaining in the cylinder 12, the intake passage 30 and the like may vary from cylinder to cylinder depending on the state of the fuel injection valve 24 and the open / close states of the intake valve 18 and the exhaust valve 19 when the engine is stopped. Therefore, even if the basic fuel injection amount Qbase is adjusted based on the initial air-fuel ratio A / Fprim as described above, if the variation in the amount of unburned gas in each cylinder 12 is large, each cylinder 12 The air-fuel ratio becomes different, and as a result, the air-fuel ratio may fluctuate. Here, during execution of the valve holding control, unburned gas travels through the cylinders 12 via the intake manifold 31 and the surge tank 32, so that the cylinders 12 and the intake passages communicating with the cylinders 12 are included. The amount of unburned gas is made uniform. However, when the execution time of the valve holding control is short, such homogenization is not sufficient, and there is a possibility that variation in the amount of unburned gas in each cylinder 12 cannot be sufficiently suppressed. Therefore, a fluctuation amount of the initial air-fuel ratio A / Fprim, for example, a difference between the maximum value and the minimum value of the initial air-fuel ratio A / Fprim within a predetermined period is detected, and the valve holding control execution period is determined based on the fluctuation amount. It can also be set.

  In such a case, since the execution period is set in consideration of variations in the amount of unburned gas in each cylinder 12, such variations can be suitably suppressed. Therefore, it is possible to appropriately suppress fluctuations in the initial air-fuel ratio A / Fprim at the time of engine start.

  When the execution period of the valve holding control is set based on the fluctuation amount of the initial air-fuel ratio A / Fprim, as shown in FIG. 9, the valve holding control is increased as the fluctuation amount of the initial air-fuel ratio A / Fprim is larger. This execution period can be set appropriately by making the execution period of (2) longer. In this case, for example, by adopting a configuration in which the threshold Cst is set to a larger value as the fluctuation amount of the initial air-fuel ratio A / Fprim is larger, the execution period of such valve holding control is set to the initial air-fuel ratio A / Fprim. Can be variably set based on the amount of fluctuation.

Further, when the fluctuation amount of the initial air-fuel ratio A / Fprim exceeds a predetermined value, the execution period of the valve holding control may be extended by a preset time.
In the above embodiment, the exhaust passage 40 is provided with the air-fuel ratio sensor 53 that outputs a signal proportional to the oxygen concentration in the exhaust. On the other hand, instead of the air-fuel ratio sensor 53, an oxygen sensor for detecting a rich state and a lean state of the oxygen concentration in the exhaust passage 40 is provided, and when the rich state is detected, a preset correction value Qcorr The basic fuel injection amount Qbase may be corrected to decrease.

  Although the basic fuel injection amount Qbase is corrected based on the initial air-fuel ratio A / Fprim as the fuel amount adjusting means, the correction process for the basic fuel injection amount Qbase may be omitted.

  In the above embodiment, the fuel injection control and the ignition control are started in the downward stroke of the piston 14. In addition, when the first explosion occurs only with the unburned gas remaining in the cylinder 12, only the ignition control is started in the ascending stroke of the piston 14 and the first explosion is generated only with the unburned gas. The fuel injection control may be started.

  The reference rotational speed NEst is desirably set to the initial explosion occurrence rotational speed described above, but even when the rotational speed near the initial explosion occurrence rotational speed is set, it is possible to suppress deterioration of exhaust properties. Is possible.

  The comparison determination process (the process of step S130 in FIG. 4) between the engine speed NE and the reference rotation speed NEst is omitted, and the comparison determination process (the process of step S140 in FIG. 4) between the count value C and the threshold value Cst is omitted. Thus, the end time of the valve holding control may be determined. Further, the comparison determination process between the count value C and the threshold value Cst (the process in step S140 in FIG. 4) is omitted, and the comparison determination process between the engine speed NE and the reference rotation speed NEst (the process in step S130 in FIG. 4) is performed. Based on this, the end time of the valve holding control may be determined.

  In the execution of the valve holding control, the intake valve 18 is held in the fully opened state, but may be held in at least the valve opened state. For example, when the valve holding control is executed, the open drive electromagnet 262 of the valve drive mechanism 20 that opens and closes the intake valve 18 is de-energized, and the intake valve 18 is held in a neutral position, so that the valve open state is made a half-open state. You may make it hold | maintain. In this case, the power consumption of the valve drive mechanism 20 during execution of the valve holding control can be suppressed.

  In the case where the electromagnetic drive unit 221 is not energized, the initial positions of the intake valve 18 and the exhaust valve 19 are set to the neutral positions. However, the present invention is not limited to such a configuration. For example, the initial position of the intake valve 18 when the electromagnetic drive unit 221 is not energized may be set to a position where the fully open state is set, and the initial position of the exhaust valve 19 may be set to a position where the fully closed state is set. In this case, the valve holding control can be executed without performing energization control to the electromagnetic drive unit 221.

  -When starting the engine, the fuel is injected in the latter half of the compression stroke, but the fuel may be injected in the intake stroke. In this case, in step S150 shown in FIG. 4, the cylinder in which the piston 14 is in the upward stroke is detected as an ignition preparation cylinder, and fuel injection control and ignition timing control are performed on the detected ignition preparation cylinder. To start. Then, after the movement direction of the piston 14 of the ignition preparatory cylinder has changed from rising to lowering, that is, after entering the intake stroke, fuel injection can be performed in the intake stroke. it can. In this case, fuel injection control is started in the same manner for the remaining cylinders, and fuel injection is performed in the intake stroke.

The structure of the valve drive mechanism 20 is an example, and in short, the present invention can be similarly applied to any drive mechanism that opens and closes the intake valve and the exhaust valve by electromagnetic force.
Moreover, in the said embodiment, the drive mechanism which opens and closes the intake valve 18 and the exhaust valve 19 by electromagnetic force was shown. However, the present invention is not limited to such a drive mechanism, and a drive mechanism that can hold the intake valve 18 in the open state and the exhaust valve 19 in the closed state when starting the engine can be employed.

  For example, when a valve drive mechanism for opening and closing the intake valve 18 and the exhaust valve 19 by a camshaft that rotates in synchronization with the rotation of the crankshaft 25 is provided, as shown in FIGS. 10 and 11, the camshaft is provided on the camshaft. The valve holding control can be performed by using a three-dimensional cam for the intake cam and the exhaust cam.

  The structure of the intake cam 310 will be described in detail with reference to FIG. FIG. 10 is a three-side view of the intake cam 310, (b) is a front view, (a) is a side view in the aa direction in (b), and (c) is a side view in the cc direction in (b). It is.

  As shown in FIG. 10, the intake cam 310 includes a normal control cam surface 320 and a valve holding control cam surface 330, which are configured as a three-dimensional cam that is gently connected by a tapered surface 340. . The cam surface for driving the intake valve 18 is switched between the normal control cam surface 320 and the valve holding control cam surface 330 by moving the intake camshaft 300 in the axial direction by the slide actuator.

  As shown in FIG. 10A, the normal control cam surface 320 opens the intake valve 18 and the base surface 322 where the intake valve 18 is closed, similar to the cam surface of a general intake cam. It is comprised by the displacement surface 324 of a cam mountain. On the other hand, in the cam surface 330 for valve holding control, all the cam surfaces with respect to the axis of the intake camshaft 300 are apexes T of the cam crest of the normal control cam surface 320 (see FIG. 10A). It is formed to have the same height. Therefore, when the slide actuator moves the intake camshaft 300 in the direction of arrow L in FIG. 10, the intake valve 18 comes into contact with the valve holding control cam surface 330 of the intake cam 310, and the intake camshaft 300 reaches the rotation angle. Regardless, the valve is always open.

  On the other hand, when the slide actuator moves the intake camshaft 300 in the direction of arrow R in FIG. 10, the intake valve 18 is driven in contact with the normal control cam surface 320 of the intake cam 310 and is synchronized with the rotation of the intake camshaft 300. It will be in the state opened and closed.

  By providing such an intake cam 310 as a drive mechanism for opening and closing the intake valve 18, the intake valve 18 can be held in the open state when the valve holding control is executed, as in the above-described embodiment. .

Similarly, the exhaust cam 410 is also configured as a three-dimensional cam having a normal control cam surface 420 and a valve holding control cam surface 430 as shown in FIG.
FIG. 11 is a three-side view of the exhaust cam 410, (b) is a front view, (a) is a side view in the aa direction in (b), and (c) is a cc direction in (b). It is a side view.

  As shown in FIG. 11, the exhaust cam 410 has a normal control cam surface 420 and a valve holding control cam surface 430, which are configured as a three-dimensional cam that is gently connected by a tapered surface 440. . Then, the cam surface for driving the exhaust valve 19 is switched between the normal control cam surface 420 and the valve holding control cam surface 430 by moving the exhaust camshaft 400 in the axial direction by the slide actuator.

  As shown in FIG. 11A, the normal control cam surface 420 opens the base valve 422 and the exhaust valve 19 where the exhaust valve 19 is closed, similar to the cam surface of a general exhaust cam. It is comprised by the displacement surface 424 of a cam mountain. In contrast, the valve holding control cam surface 430 is formed so that all the cam surfaces have the same height as the base surface 422 of the normal control cam surface 420 with respect to the axial center of the exhaust camshaft 400. Yes. For this reason, when the slide actuator moves the exhaust camshaft 400 in the direction of arrow L in FIG. 11, the exhaust valve 19 comes into contact with the valve holding control cam surface 430 of the exhaust cam 410 and the rotational angle of the exhaust camshaft 400 is reached. Regardless, the valve is always closed.

  On the other hand, when the slide actuator moves the exhaust camshaft 400 in the direction of arrow R in FIG. 11, the exhaust valve 19 is driven in contact with the normal control cam surface 420 of the exhaust cam 410 and is synchronized with the rotation of the exhaust camshaft 400. It will be in the state opened and closed.

  By providing such an exhaust cam 410 as a drive mechanism for opening and closing the exhaust valve 19, it is possible to hold the exhaust valve 19 in a closed state when executing the valve holding control, as in the above embodiment. .

In the above embodiment, two intake valves 18 and two exhaust valves 19 are provided for each cylinder 12, but the number thereof can be arbitrarily changed.
-When executing the valve holding control, both of the two intake valves 18 provided for each cylinder 12 are held open. In addition, at least one of the plurality of intake valves 18 provided for each cylinder 12 may be held open. Even in this case, the unburned gas remaining in each cylinder 12 can travel between the cylinders 12.

  In the above embodiment, the engine 10 is a cylinder injection internal combustion engine. In addition, even if the engine 10 is an intake port injection type internal combustion engine in which fuel is injected into the intake port, there is a risk of deterioration of exhaust properties due to fuel leaking from the fuel injection valve. That is, in an intake port injection type internal combustion engine, fuel adheres and remains in the intake passage, and therefore, until the first explosion occurs at the time of starting the engine, the adhering fuel, that is, vaporized fuel caused by the residual fuel is not yet present. There is a risk that exhaust properties are deteriorated by being discharged into the exhaust passage while still burning. Therefore, even if the engine 10 is an intake port injection type internal combustion engine, by applying the present invention to its control device, it is possible to obtain the same operation and effect as in the above embodiment, so that it remains in the intake passage. Deterioration of exhaust properties due to fuel being discharged as unburned gas when the engine is started can be suppressed. Incidentally, even if the engine 10 includes a fuel injection valve that directly injects fuel into the combustion chamber 15 and a fuel injection valve that injects fuel into the intake port 16, the present invention can be similarly applied. .

  In the above embodiment, the ignition plug 23 is provided in each cylinder and the ignition control is executed by the ECU 90. However, the present invention is similarly applied to an engine that does not require an ignition plug such as a diesel engine. Can be applied.

  The present invention can be similarly applied to a control device for an internal combustion engine in which the number of cylinders, cylinder arrangement, or ignition order is different from the engine 10.

1 is a schematic diagram showing a schematic configuration of an engine to which a control device for an internal combustion engine according to the present invention is applied. The schematic diagram which shows the structure of the intake system of this engine, and an exhaust system. Sectional drawing of the valve drive mechanism in the embodiment. The flowchart which shows the process sequence about starting control of the internal combustion engine in the embodiment. 4 is a flowchart showing a processing procedure for setting a correction value for a fuel injection amount in the embodiment. The graph which shows the relationship between the initial air fuel ratio A / Fprim and correction value Qcorr. The timing chart which shows the relationship between the engine speed NE and the switching timing of a valve control mode. The timing chart which shows the relationship between the timing of the up-and-down movement of a piston, and the switching timing of the valve control mode in each cylinder. The graph which shows the relationship between the variation | change_quantity of an initial stage air fuel ratio, and the execution period of valve | bulb holding | maintenance control in the modification of the embodiment. It is a three-view figure of the intake cam with which the valve drive mechanism in the modification of the embodiment is provided, (a) is a front view, (b) is a left side view, (c) is a right side view. It is a three-view figure of the exhaust cam with which the valve drive mechanism in the modification of the embodiment is provided, (a) is a front view, (b) is a left side view, (c) is a right side view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Engine, 11 ... Cylinder block, 12a ... 1st cylinder, 12b ... 2nd cylinder, 12c ... 3rd cylinder, 12d ... 4th cylinder, 13 ... Cylinder head, 14 ... Piston, 15 ... Combustion chamber, 16 ... Intake Port, 17 ... Exhaust port, 18 ... Intake valve, 19 ... Exhaust valve, 19a ... Valve shaft, 19b ... Umbrella, 20 ... Valve drive mechanism, 23 ... Ignition plug, 24 ... Fuel injection valve, 25 ... Crankshaft, 29 DESCRIPTION OF SYMBOLS ... Connecting rod, 30 ... Intake passage, 31 ... Intake manifold, 32 ... Surge tank, 33 ... Throttle valve, 40 ... Exhaust passage, 41 ... Exhaust manifold, 42 ... Catalytic converter, 51 ... Crank angle sensor, 52 ... Air flow meter, 53 ... Air-fuel ratio sensor, 54 ... Displacement sensor, 55 ... Water temperature sensor, 56 ... Igni Switch (IG switch), 80 ... starter motor, 90 ... electronic control unit (ECU), 100 ... timing rotor, 215 ... valve seat, 221 ... electromagnetic drive, 222 ... lower retainer, 224 ... lower spring, 226 ... armature shaft 228 ... Armature, 230 ... Upper partition, 232 ... Upper core, 234 ... Lower core, 236 ... Upper cap, 238 ... Upper spring, 240, 244 ... Groove, 242 ... Upper coil, 246 ... Lower coil, 261 ... Electromagnet for closing drive, 262 ... Electromagnet for opening drive, 300 ... Intake cam shaft, 310 ... Intake cam, 320 ... Normal control cam surface, 322 ... Base surface, 324 ... Displacement surface, 330 ... Valve holding control cam surface, 340 ... Tapered surface, 400 ... exhaust cam shaft, 410 ... exhaust cam, 420 ... normal Patronized cam surface 422 ... base surface, 424 ... displacement surface, 430 ... valve holding control cam surface, 440 ... tapered surface.

Claims (11)

In an internal combustion engine comprising a plurality of cylinders and a drive mechanism that opens and closes an exhaust valve and an intake valve provided in each cylinder, the control device that performs opening and closing control of each valve by the drive mechanism,
A control device for an internal combustion engine, wherein during the cranking of the internal combustion engine, valve holding control for holding all the exhaust valves in a fully closed state and holding the intake valve in a valve open state is executed. The control device for an internal combustion engine according to claim 1, wherein when performing the valve holding control, all of the intake valves of each cylinder are held open. The control apparatus for an internal combustion engine according to claim 1 or 2, wherein when performing the valve holding control, the intake valve is held in a fully open state. The control device for an internal combustion engine according to any one of claims 1 to 3,
An air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust and a fuel amount adjusting means for adjusting the amount of fuel supplied to the cylinder are provided, and the opening operation of the exhaust valve is started after the execution of the valve holding control is finished. A control device for an internal combustion engine, characterized in that the fuel injection amount at the next engine start is adjusted based on the air-fuel ratio detected after the operation is performed. The control device for an internal combustion engine according to claim 4, wherein the fuel injection amount is reduced as the richness of the air-fuel ratio is higher. The control apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the valve holding control is terminated when an engine rotation speed during cranking is equal to or higher than an initial explosion occurrence rotation speed. In addition to the condition that the engine rotation speed is equal to or higher than the initial explosion occurrence rotation speed, the valve holding control is terminated when any one of the pistons goes up, and the valve holding control is performed. The control device for an internal combustion engine according to claim 6, wherein the exhaust valve and the intake valve of a cylinder in which the piston is in an ascending stroke with the end of are closed. The control apparatus for an internal combustion engine according to any one of claims 4 to 7, wherein an execution period of the valve holding control at the next engine start is set based on a fluctuation amount of the air-fuel ratio. The control device for an internal combustion engine according to claim 8, wherein the execution period is lengthened as the fluctuation amount is larger. The control device for an internal combustion engine according to any one of claims 1 to 9, wherein the drive mechanism is a mechanism that opens and closes the exhaust valve and the intake valve by electromagnetic force. The control device for an internal combustion engine according to any one of claims 1 to 10, wherein the internal combustion engine is a direct injection internal combustion engine in which fuel is directly supplied into a cylinder.

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