JPH05321702A - Valve system control device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Purpose] A variable valve timing mechanism is used to improve exhaust efficiency and fuel efficiency in low engine speed and low load operation regions. [Structure] When the valve timing is set to a low speed valve timing, the exhaust valve is closed in the first half of the exhaust process, and the intake valve is opened when the in-cylinder pressure becomes substantially atmospheric pressure. When the valve timing is set to the high speed valve timing, the intake / exhaust valve is opened / closed at substantially normal valve timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve operating control system for an internal combustion engine, and more particularly to a valve operating control system for an internal combustion engine having valve timing switching means capable of switching the valve timing of intake and exhaust valves of the internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas recirculation control system is widely known in which a part of exhaust gas of an internal combustion engine is recirculated to an intake passage to reduce nitrogen oxide (NOx) which is one of harmful gas generated from the engine. Has been.

In order to improve fuel efficiency, it is necessary to increase the maximum value of the combustible air-fuel ratio, that is, the lean limit of combustion. For that purpose, the air-fuel mixture around the spark plug in the combustion chamber is made fuel-rich, and the piston It is known that it is preferable to carry out so-called stratified combustion by making the air-fuel mixture on the side lean. In the exhaust gas recirculation control system, a technique has already been proposed in which exhaust gas recirculation gas (hereinafter referred to as “EGR gas”) and fresh air are introduced into the combustion chamber from different intake ports to achieve stratified combustion. (For example, Japanese Utility Model Laid-Open No. 62-175248,
Japanese Utility Model Laid-Open No. 64-34434, etc.) (hereinafter referred to as "first conventional example").

On the other hand, paying attention to the exhaust efficiency of the internal combustion engine, it is known that the HC concentration in the exhaust gas generally shows particularly high peaks in the early and late stages of the exhaust stroke of the engine. A technology has already been proposed that effectively reduces the HC emissions in exhaust gas with a small amount of exhaust gas recirculation by causing exhaust gas recirculation only in the latter stage of the exhaust stroke of an engine in which the HC concentration in the gas is particularly high. (For example, JP-A-1-244155) (hereinafter,
"Second conventional example").

That is, since the fresh air sucked in the intake stroke is compressed in the compression stroke and enters the topland clearance (the clearance surrounded by the piston, the piston ring and the cylinder), the fresh air explodes thereafter. After passing through the stroke, the fuel is ejected into the combustion chamber through the top land gap only after entering the exhaust stroke. However, since the combustion has already ended at this time, this fresh air is exhausted as it is without contributing to combustion, and the timing of this exhaust corresponds to the latter half of the exhaust stroke. Therefore, in the second conventional example, the exhaust gas recirculation is performed only near the latter stage of the exhaust stroke to suppress the emission of HC that is an unburned component.

[0006]

However, in the above-mentioned first conventional example, since both the EGR gas and the fresh air are sucked in during the intake stroke, the EGR gas and the fresh air are sucked in. After being sucked into the cylinder due to their inherent velocity energy, the combustion chamber becomes a mixed state of EGR gas and fresh air, and a desired stratified combustion state cannot be obtained in the combustion chamber. was there.

Further, since the combustion gas is once caused to flow out of the cylinder, it is possible to completely prevent the thermal activation energy of the combustion gas from flowing out of the wall surface while flowing through the intake port or the like. There was a problem that it could not be done.

Further, in the second conventional example, it is difficult to completely suppress the discharge of the unburned component (HC) generated from the top land gap, and the discharged HC is discharged. Since it is difficult to selectively recirculate the exhaust gas into the exhaust gas, there is a problem that there is room for further improving the exhaust efficiency.

By the way, an internal combustion engine having a variable valve timing mechanism in which the valve timing opening time of the intake valve and the exhaust valve of the engine and the valve lift amount can be switched according to the engine speed has been already known by the applicant of the present application. (For example, Japanese Patent Laid-Open No. 2-102347).

In the internal combustion engine having the variable valve timing mechanism, the valve timing is a high speed valve timing suitable for a high rotation range and a low speed valve timing suitable for a low rotation range according to the engine operating conditions such as engine speed and engine load. By switching to and, the intake and intake efficiency (combustion efficiency) can be improved, and the engine output can be increased.

The present invention is intended to solve the above-mentioned problems by utilizing such a variable valve timing mechanism, and aims to improve the exhaust efficiency and the fuel efficiency when the engine is running at low speed and in the low load operating range. An object of the present invention is to provide a valve operation control device for an internal combustion engine that can perform the operation.

[0012]

In order to achieve the above-mentioned object, a valve operating system for an internal combustion engine according to the present invention is a low speed valve valve timing of an intake valve and an exhaust valve of the internal combustion engine suitable for at least a low rotation speed region. A valve timing switching means capable of switching between a valve timing and a high speed valve timing suitable for a high rotation region is provided, and when the valve timing is set to a low speed valve timing by the valve timing switching means, the exhaust valve is a piston. When the valve timing is set to the high speed valve timing by the valve timing switching means while the valve is closed at the predetermined crank angle position before the top dead center, the exhaust valve moves from the predetermined crank angle position to the piston top dead center. Close at the crank angle position on the side.

Further, the predetermined crank angle position is specifically set to a crank angle position corresponding to the first half of the exhaust stroke.

Further, according to the present invention, when the valve timing is set to the low speed valve timing by the valve timing switching means, the exhaust valve is closed at the first predetermined crank angle position before the piston top dead center. When the intake valve is opened at the second predetermined crank angle position after the piston top dead center and the valve timing is set to the high speed valve timing by the valve timing switching means, the exhaust gas is discharged. The valve closes at a crank angle position closer to the piston top dead center than the first predetermined crank angle position, and the intake valve opens at a crank angle position closer to the piston top dead center than the second predetermined crank position. It is characterized by doing.

Further, the first predetermined crank angle position is specifically set to a crank angle position corresponding to the first half of the exhaust stroke, while the second predetermined crank angle position corresponds to the cylinder pressure. The crank angle position is set to correspond to the time when the atmospheric pressure is reached.

[0016]

According to the above construction, the exhaust valve is closed in the first half of the exhaust process when the valve timing is set to the low speed valve timing, and is set to the low speed valve timing when the high speed valve timing is set. The valve is closed at a closing timing that is later than the closing timing.

Further, the intake valve is opened when the valve timing is set to the low speed valve timing and the valve is opened when the in-cylinder pressure becomes substantially the same as the atmospheric pressure, and is set to the high speed valve timing. At this time, the valve is opened at an opening timing faster than the opening timing of the low speed valve timing.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of an essential part showing an embodiment of a valve operating control system for an internal combustion engine according to the present invention.

In the figure, reference numeral 1 denotes a DOHC in-line four-cylinder internal combustion engine (hereinafter referred to simply as "engine"). The engine 1 includes a piston 3 to which three piston rings 2 are fixed, and A cylinder block 5 is formed by arranging four fitted cylinders 4 in parallel, and a cylinder head 6 connected above the cylinder block 5. Further, the cylinder head 6 is formed with a pair of intake ports 7 and a pair of exhaust ports 8 at portions corresponding to above the piston 3, and the intake ports 7 are opened on one side surface of the cylinder head 6. Connected to the intake port (not shown),
The exhaust port 8 is connected to an exhaust port 9 that opens on the other side surface of the cylinder head 6.

Valve guide 1 fixed to cylinder head 6
0 and 11 include a pair of intake valves 12a and 12b and an exhaust valve 1
3a and 13b are inserted, and the intake port 7 and the exhaust port 8 can be opened and closed. The combustion chamber 1 is surrounded by the portion surrounded by the intake port 7 and the exhaust port 8 above the piston 3.
4 are formed.

In the following description, since the valve mechanism on the intake side and the valve mechanism on the exhaust side have the same structure, only the structure on the exhaust side will be described, and the structure on the intake side will be omitted.

That is, in FIG. 1, the exhaust valve 13
Valve springs 16a and 16b are contracted between the flange portions 15a and 15b of a and 13b and the cylinder head 6, and the exhaust valves 13a and 13b are moved upward in the drawing by the valve springs 16a and 16b. ) Is urged towards.

On the other hand, above the cylinder head 6, a cam shaft 19 to which a pair of low speed cams 17a and 17b and a high speed cam 18 are fitted is rotatably arranged. The cam shaft 19 is connected to a crank shaft (not shown) via a timing belt (not shown).

The cams 17a, 17b, 18 and the exhaust valve 1
A hydraulically driven valve unit 20 is interposed between 3a and 13b. The hydraulically driven valve unit 20 includes an exhaust valve 13
Solenoid valve 2 for performing valve timing switching control of a and 13b
1 and a switching valve 22 for switching valve timing by switching high / low of hydraulic pressure, and a predetermined hydraulic pressure is supplied to the hydraulically driven valve unit 20 from the oil tank 23 via the oil pump 24 and the oil passage 25. Supplied.

Further, the hydraulically driven valve unit 20 includes an electronic control unit (hereinafter referred to as "ECU") 2
A control signal (θOFF) for electrically controlling the closing timing of the exhaust valve 13 is supplied from the ECU 26. As a result, the valve timings of the exhaust valves 13a and 13b are the high speed valve timing (high speed V / T) suitable for the high speed rotation range of the engine and the low speed valve timing (low speed V / T) suitable for the low speed rotation range of the engine. It is possible to switch to stages.

A lift sensor 27 for detecting the lift amount of the exhaust valve 13 is provided in the vicinity of the flange portion 15 of the exhaust valve 13, and the detection signal is supplied to the ECU 26.

A throttle valve opening (θTH) sensor 28 is connected to the ECU 26, and the θTH sensor 28 is connected.
Detects the valve opening degree θTH of the throttle valve and supplies the electric signal to the ECU 26.

Further, the ECU 26 is informed of the cylinder discrimination (CY).
L) sensor 29 and crank angle (CRK) sensor 30 are electrically connected. Cylinder discrimination (CYL) sensor 2
9 and the crank angle (CRK) sensor 30 are connected to the engine 1
Of the CYL sensor 29 is mounted at a predetermined position around the cam shaft or the crank shaft, respectively, and the CYL sensor 29 outputs a pulse signal (hereinafter referred to as "CYL determination signal") at a predetermined crank angle position of a specific cylinder for every two rotations of the crank shaft of the engine 1. Output),
The CRK sensor 30 has a predetermined crank angle (for example, 30
A pulse signal (hereinafter referred to as “CRK pulse signal”) is output every (°), and these pulse signals are supplied to the ECU 26.

The atmospheric pressure (PA) sensor 31 is arranged at a proper position of the engine, detects the atmospheric pressure PA, and supplies the detection signal to the ECU 26.

Thus, the ECU 26 has an input circuit having a function of shaping the waveforms of the input signals from the various sensors described above, correcting the voltage level to a predetermined level, and converting an analog signal value into a digital signal value. A central processing circuit (hereinafter referred to as "CPU") and R for storing various calculation programs executed by the CPU, various maps, calculation results, etc.
The storage means comprises an OM and a RAM, and an output circuit for supplying a drive signal to the hydraulically driven valve unit 20.

FIG. 2 is a detailed view of the exhaust side valve operating mechanism (a view as seen from the arrow (A-A) in FIG. 1), in which the high speed cam 18 and a pair of low speed cams are provided on the cam shaft 19, as described above. Cams 17a, 17
b and the cam shaft 19 are integrally fitted to the outside. Further, the rocker shaft 32 is disposed in parallel with the cam shaft 19, and a pair of drive rocker arms 33a and 33b and a free rocker arm 34 are pivotally supported on the rocker shaft 32. The cams 17a, 17b, 18 can contact the rocker arms 33a, 33b, 34, and the exhaust valves 13 are rotated by the cams 17a, 17b, 18 to rotate.
Control the on-off valves of a and 13b.

However, the valve operating mechanism has a connection switching mechanism for switching the valve timing.

Specifically, as shown in FIG. 3, the connection switching mechanism 35 includes a first switching pin 36 which enables the first drive rocker arm 33a and the free rocker arm 34 to be connected.
And the free rocker arm 34 and the second drive rocker arm 3
3b, a second switching pin 37, a restriction pin 38 for restricting the movement of the first and second switching pins 36, 37, and a resilient biasing force of these pins 36 to 38 toward the decoupling side. And a return spring 39 for

The first drive rocker arm 33a is provided with a bottomed first guide hole 40, which is open on the free rocker arm 34 side, in parallel with the rocker shaft 32.
The first switching pin 36 is slidably fitted in the first guide hole 40, and the hydraulic chamber 41 is provided between the one end side of the first switching pin 35 and the closed end of the first guide hole 40. Well defined. Further, a passage 42 communicating with the hydraulic chamber 41 is provided through the first drive rocker arm 33a, and the rocker shaft 32
An oil supply passage 43 is provided in the. The oil supply passage 43 is the first
Regardless of the rocking state of the drive rocker arm 33a
Is constantly communicated with the hydraulic chamber 41 via.

The free rocker arm 34 has a guide hole 44 facing the first guide hole 40.
A second switching pin 37, which is provided so as to extend through both side surfaces of the first and second ends and is capable of abutting against the first switching pin 36, is slidably fitted in the guide hole 44. ..

In the second drive rocker arm 33b, a second guide hole 45 is formed at a position facing the guide hole 44 in parallel with the rocker shaft 32, and the other end of the second switching pin 37 is formed. A disc-shaped restricting pin 38 that comes into contact with is slidably fitted in the second guide hole 45. Further, a guide cylinder 46 is fitted to the other end of the second guide hole 45,
A shaft portion 47 slidably fitted in the guide cylinder 46 is provided so as to project from the restriction pin 38. Further, the return spring 39 is contracted between the guide cylinder 46 and the restriction pin 38, and the return spring 39 elastically urges the pins 36 to 38 toward the hydraulic chamber 41 (disconnection).

In the connection switching mechanism 35 thus configured, the first switching pin 36 slides toward the guide hole 44 (to the right in the figure) as the hydraulic pressure in the hydraulic chamber 41 increases. The second switching pin 37 has the second guide hole 4
Sliding to the 5 side (right side in the figure), each rocker arm 33
a, 33b, and 34 are connected. When the hydraulic pressure in the hydraulic chamber 41 becomes low, one end of the first switching pin 36 is on the side of the first guide hole 40 due to the elastic urging force of the return spring 39 toward the hydraulic chamber 41 side (left side in the drawing). The second switching pin 37 is accommodated in the guide hole 44 while being in contact with the portion, and the connection state of the rocker arms 33a, 33b, 34 is released.

The oil supply passage 43 in the rocker shaft 32 is also used.
Is connected to an oil pump 24 via a switching valve 22, and the switching operation of the switching valve 22 raises or lowers the hydraulic pressure in the oil supply passage 43, and thus the hydraulic pressure in the hydraulic chamber 41 of the connection switching mechanism 35. Can be switched. This switching valve 22 is connected to the solenoid valve 21, and the switching operation of the switching valve 22 is E
It is controlled by the CU 26 via the solenoid valve 21.

The exhaust side valve operating mechanism of the engine 1 configured as described above operates as follows.

When the ECU 26 outputs a valve opening command signal to the solenoid valve 21, the solenoid valve 21 opens and the switching valve 22 opens to raise the oil pressure in the oil supply passage 43.
As a result, the connection switching mechanism 35 operates to bring the rocker arms 33a, 33b, 34 into the connected state, and the high speed cam 1
8, the rocker arms 33a, 33b, 34 are integrally operated (FIG. 2 shows this state), and the pair of exhaust valves 13a, 13b operate at high speed with a relatively large opening period and lift amount. It opens and closes at the valve timing.

On the other hand, when the ECU 26 outputs a valve closing command signal to the solenoid valve 21, the solenoid valve 21 and the switching valve 22.
Is closed and the oil pressure in the oil supply passage 43 decreases. As a result, the connection switching mechanism operates in reverse to the above, the connection state of each rocker arm 33a, 33b, 34 is released (FIG. 3 shows this state), and the low speed cams 17a, 17b respectively respond. The rocker arms 33a and 33b are actuated, and the pair of intake valves 13a and 13b are actuated at a low valve timing in which the valve opening period and the lift amount are relatively small.

In the valve operating control system for the internal combustion engine, however, as shown in FIG. 4, the intake / exhaust valves 12 and 13 operate as follows in accordance with the set state of the valve timing.

That is, the valve timing is low speed V / T.
When set to, the exhaust valves 13a and 13b are normally opened from the crank angle position near the piston bottom dead center (BTDC 180 °) at which the explosion stroke ends, and the exhaust stroke first half, that is, BTDC 90 ° is reached. Exhaust valve 1
3a and 13b are closed. At this time, the intake valves 12a and 12b
Since the valve is closed, the compression begins while the exhaust gas remains inside the cylinder during the exhaust stroke. Then, the exhaust gas remaining in the cylinder is compressed until the exhaust stroke ends, and enters the intake stroke and expands. Next, in the intake stroke, piston 3
Is lowered, the cylinder pressure is reduced, and the cylinder pressure PA
The intake valve 12 (when detected by the PA sensor 31) becomes substantially the same as the atmospheric pressure (for example, ATDC 90 °).
The valves a and 12b are opened. And thus, the intake valve 12
After the valves a and 12b are opened and the cylinder pressure PA falls below the atmospheric pressure, the intake of fresh air into the cylinder begins. That is,
The fresh air is pressure-regulated by the throttle valve, flows into the combustion chamber 14, and is slowly drawn into the combustion gas remaining in the combustion chamber 14. That is, by maintaining the state where the exhaust gas remains in the cylinder, so-called internal EGR is achieved, and stratification (stratification) is obtained by the fresh air from the intake port and the combustion gas above the piston. Moreover, the intake speed of the fresh air is determined by the fact that gas is already present in the cylinder at the time of entering the intake stroke, and the opening timing of the intake valve is in the middle of the intake stroke. Even when the degree is small, the negative pressure generated in the cylinder is low, and therefore the inflow velocity is also low, and the flow in the cylinder that prevents stratification is prevented.

As described above, the combustion gas remaining in the cylinder acts so as to prevent the fresh air newly sucked by the achievement of the internal EGR from reaching the vicinity of the piston 3. Fresh air is prevented from entering and the generation of HC, which is an unburned component, is suppressed from the generation source. In addition, the amount of gas remaining in the cylinder at the start of compression is high, the in-cylinder compression at the start of compression is high, and the energy required for the process of inhaling fresh air is small, The consumption rate can be reduced.

When the valve timing is set to the high speed V / T, the overlap period O is almost normal.
The intake / exhaust valve operates at a valve timing having VT.

That is, the closing timing of the exhaust valves 13a and 13b is closed later than the closing timing of the low speed V / T, and the opening timing of the intake valves 12a and 12b is the opening timing of the low speed V / T. By opening the valve earlier than the timing, deterioration of the engine output characteristics is prevented.

FIGS. 5 and 6 show low speed V / T and high speed V.
3 is a PV diagram at the time of / T, where the vertical axis is the pressure P and the horizontal axis is the stroke volume V.

When the valve timing is set to the low speed V / T, the exhaust valve 13 is opened at the time when the in-cylinder pressure shows a pressure value slightly larger than the atmospheric pressure PA, and the exhaust valve 13 enters the exhaust stroke. Piston 3 moves from BDC (bottom dead center) to TDC
The valve closes in the first half while moving to (top dead center) (the cylinder pressure at this time is approximately atmospheric pressure). Then, since the exhaust valve 13 is closed, the in-cylinder pressure gradually increases up to TDC after that, but the in-cylinder pressure again approaches the atmospheric pressure because the piston descends. Then, the intake valve 12 opens at the time when the in-cylinder pressure becomes substantially atmospheric pressure, and the intake valve 12 becomes when the in-cylinder pressure during the movement of the piston 3 from BDC to TDC becomes substantially the same as the atmospheric pressure PA. After closing the valve, during the compression stroke and the explosion stroke, the illustrated work is executed on the PV diagram (hatched portion), and the exhaust valve 13 is opened again.

When the valve timing is set to the high speed V / T, the exhaust valve 13 opens at the time when the in-cylinder pressure shows a value slightly larger than the atmospheric pressure PA, as in the low speed V / T. The exhaust valve 13 is closed near the piston TDC in the exhaust stroke, and the intake valve 12 is opened.

Then, the intake valve 12 is closed at the time when the in-cylinder pressure becomes approximately atmospheric pressure PA during the movement from BDC to TDC, as in the above-described low speed V / T, and then during the compression stroke and the explosion stroke, PV is closed. The illustrated work is performed on the diagram (hatched portion), and the exhaust valve 13 opens again.

[0052]

As described in detail below, in the valve operating system for an internal combustion engine according to the present invention, the valve timing of the intake valve and the exhaust valve of the internal combustion engine is a low speed V / T suitable for at least a low rotation speed region. A valve timing switching means capable of switching to a high speed V / T suitable for a high rotation region is provided, and when the valve timing is set to a low speed V / T by the valve timing switching means, the exhaust valve is above the piston. When the valve timing is set to the high speed V / T by the valve timing switching means while the valve is closed at the predetermined crank angle position before the dead center, the exhaust valve is at the piston top dead center from the predetermined crank angle position. Since the valve closes at the crank angle position on the side, at a low speed V / T, there is a large amount of in-cylinder for a predetermined period from the closing of the exhaust valve to the opening of the intake valve. It will be gas-gas stagnates, N
The emission of harmful components such as Ox and HC to the atmosphere can be further suppressed. In addition, the amount of gas remaining in the cylinder at the start of compression is large, the pressure in the cylinder at the start of compression is high, and the amount of energy required for the process of inhaling fresh air is small. The consumption rate can be reduced. In addition, since the desired stratified combustion is possible, fresh air can be positioned near the cylinder head even during idle operation or in a low load operation area, which facilitates ignition and the active heat of the exhaust gas. It can be used without dissipating energy, and the fresh air that is taken in is activated by the exhaust gas before ignition, so that combustion can be improved.

Specifically, the above-mentioned effect can be easily realized by setting the predetermined crank angle position to a crank angle position corresponding to the first half of the exhaust stroke.

Further, when the valve timing is set to the low speed V / T by the valve timing switching means, the exhaust valve is closed at the first predetermined crank angle position before the piston top dead center, and While the intake valve opens at the second predetermined crank angle position after the top dead center of the piston, while the valve timing is set to the high speed valve timing by the valve timing switching means, the exhaust valve is The valve is closed at the crank angle position on the piston top dead center side from the first predetermined crank angle position,
Moreover, the intake valve is opened at a crank angle position closer to the piston top dead center than the second predetermined crank position, and the first predetermined crank angle position is a crank angle position corresponding to the first half of the exhaust stroke. On the other hand, since the second predetermined crank angle position is set to the crank angle position at the time when the in-cylinder pressure becomes substantially atmospheric pressure, the in-cylinder generated negative pressure is maintained even when the throttle valve opening is narrow. The flow rate is low, and therefore the inflow velocity is also low, and in-cylinder flow that prevents stratification is prevented. Therefore, the combustion gas remaining in the cylinder acts to prevent freshly sucked fresh air from reaching the vicinity of the piston, and is generated by the fresh air entering the topland gap.
The generation of HC due to the unburned fuel discharged is more effectively prevented.

Further, according to the present invention, unlike the prior art, the exhaust gas is not recirculated to the outside, so that a deposit due to the exhaust recirculation gas does not occur.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram showing an embodiment of a valve operating control system for an internal combustion engine according to the present invention.

FIG. 2 is a view on arrow (A-A) in FIG.

FIG. 3 is a view taken along the line (BB) of FIG.

FIG. 4 is a characteristic diagram for explaining the operation of intake and exhaust valves of the valve operating control system for an internal combustion engine according to the present invention.

FIG. 5 is a PV diagram when operating at low speed V / T.

FIG. 6 is a PV diagram when operating at high speed V / T.

[Explanation of symbols]

 1 Internal Combustion Engine 20 Hydraulic Drive Unit (Valve Timing Switching Means) 26 ECU 30 CRK Sensor

Claims (4)

[Claims] 1. A valve timing switching means capable of switching the valve timing of an intake valve and an exhaust valve of an internal combustion engine to at least a low speed valve timing suitable for a low rotation range and a high speed valve timing suitable for a high rotation range, When the valve timing is set to the low speed valve timing by the valve timing switching means,
While the exhaust valve is closed at a predetermined crank angle position before piston top dead center, while the valve timing is set to a high speed valve timing by the valve timing switching means, the exhaust valve is set to the predetermined crank angle position. A valve operating control device for an internal combustion engine, wherein the valve is closed at a crank angle position closer to the piston top dead center. 2. The valve operation control device for an internal combustion engine according to claim 1, wherein the predetermined crank angle position is set to a crank angle position corresponding to the first half of the exhaust stroke. 3. A valve timing switching means capable of switching the valve timing of an intake valve and an exhaust valve of an internal combustion engine to at least a low speed valve timing suitable for a low rotation range and a high speed valve timing suitable for a high rotation range, When the valve timing is set to the low speed valve timing by the valve timing switching means,
The exhaust valve closes at a first predetermined crank angle position before piston top dead center, and the intake valve opens at a second predetermined crank angle position after piston top dead center, while the valve timing Is set to a high speed valve timing by the valve timing switching means, the exhaust valve is closed at the crank angle position closer to the piston top dead center than the first predetermined crank angle position, and the intake valve is A valve operating control device for an internal combustion engine, wherein the valve is opened at a crank angle position closer to the piston top dead center than the second predetermined crank position. 4. The first predetermined crank angle position is set to a crank angle position corresponding to the first half of the exhaust stroke, while the second predetermined crank angle position has an in-cylinder pressure of substantially atmospheric pressure. 4. The valve operation control device for an internal combustion engine according to claim 3, wherein the crank angle position is set to a time point.