JP2741267B2 - Engine intake and exhaust control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake / exhaust control device for an engine, and more particularly, to an intake / exhaust control device that is closed in each cylinder independent intake passage when the engine is idling. The present invention relates to a fuel cell system in which a minimum value and a maximum value of an overlap amount can be set to be large to improve fuel efficiency and emission at least under a middle load state in a high speed range while ensuring combustion stability during idling.

(Prior art)

Generally, an intake / exhaust overlap in which the exhaust valve open period and the intake valve open period partially overlap is provided because it is necessary to inhale necessary intake in an intake stroke of an engine and scavenge burned gas in an exhaust stroke. However, the amount of overlap between the intake and exhaust has a great effect on engine performance as well as intake performance and scavenging performance.

In the idle state, it is necessary to reduce the intake / exhaust overlap amount in order to secure combustion stability, that is, idle stability. That is, when idling, the amount of air-fuel mixture is small and combustion stability is not sufficient, and since the boost negative pressure is large, burned gas flows back from the exhaust system and tends to remain more. The stability is significantly reduced.

On the other hand, it has been considered that, in a high load state, if the intake / exhaust overlap amount is increased, the intake inertia effect also works to increase the intake efficiency and enhance the torque characteristics.

Therefore, recently, a variable valve timing mechanism capable of changing the valve timing of the intake valve (or a variable valve timing mechanism for the exhaust valve) may be provided. Is set to a small value, and the intake / exhaust overlap amount is set large in other operating states (see JP-A-62-191636 and JP-A-63-195325). ).

The variable valve timing mechanism is a sleeve-shaped gear piston having mutually opposite helical splines meshed with the shaft end and the pulley on both inside and outside surfaces between the shaft end of the intake camshaft and the pulley. , And the relative phase between the intake camshaft and the pulley is changed by driving the gear piston in the axial direction by hydraulic pressure.
In this type of conventional variable valve timing mechanism, the intake / exhaust overlap amount is switched between two stages of “small” and “large”. "Small" is set at about 20 ° crank angle, and "Large" is set at about 40 ° crank angle.

On the other hand, recently, in order to facilitate idle adjustment of the throttle valve and increase idle stability, a throttle valve is provided in a common intake passage for all cylinders as described in, for example, JP-A-63-195325. A cylinder-independent intake passage provided with an intake control valve that is controlled to be closed at least in an idle state has also been put to practical use.

[Problems to be solved by the invention]

Conventionally, the effect of the intake and exhaust overlap amount on the engine performance has not been sufficiently studied, and the intake and exhaust overlap amount has been studied only from the viewpoint of securing idle stability and improving intake efficiency. thought to be improved HC and nO _X in the exhaust gas, fuel economy by appropriately controlled according to the overlap amount in the operating state has not been proposed at all.

First, the effect of the intake and exhaust overlap on engine performance will be considered. As shown in FIGS. 8, 9 and 10 according to the embodiment of the present invention, it is basically desirable to increase the intake / exhaust overlap amount with the increase of the engine speed for the full open torque. (See FIG. 8).

The NO _X, in response to the intake and exhaust overlap amount becomes larger, the residual amount of exhaust gas (including reverse flow fraction from the exhaust system) is increased (in particular, because at the time of low load is large boost negative pressure exhaust gas This internal EG
Combustibility is reduced by the R action, and NO _X is reduced (see FIGS. 9 and 10).

As for HC, when the load condition shown in FIG. 9 is constant, the HC decreases as the intake / exhaust overlap amount decreases in the low rotation speed region, whereas the HC intake amount increases in the high rotation speed region. HC decreases as the temperature decreases. In the case where the rotation speed is constant as shown in FIG. 10, the HC decreases as the intake / exhaust overlap amount decreases in a low load state, whereas the HC decreases.
Under high load conditions, the larger the intake / exhaust overlap amount,
HC is reduced. As described above, for the HC, it is desirable to increase the intake / exhaust overlap amount in accordance with the increase in the engine speed or the load.

In addition, the suction pumping loss is reduced as the residual exhaust gas amount increases, and the fuel efficiency is improved as the HC is reduced.
Incidentally, NO in normal external EGR employed for _X reduced, since there is no guarantee for recirculating high concentration unburned gas generated by the final stage in the cylinder wall adhesion fuel exhaust stroke into the combustion chamber HC
The effect of reducing the pumping loss is not obtained, and the effect of reducing the suction pumping loss is weakened because the temperature of the recirculated exhaust gas is lowered.

Therefore, it is desirable to increase the intake / exhaust overlap amount as the rotational speed increases and as the load increases. Therefore, it is conceivable to increase the stroke of the gear piston of the variable valve timing mechanism. However, in this case, the switching time of the intake / exhaust overlap amount becomes longer and the response is lacking. Not preferred. Therefore, if the intake / exhaust overlap amount in the idle state is increased in order to increase the maximum value of the intake / exhaust overlap amount, combustion stability in the idle state cannot be ensured.

As described above, in the engine equipped with the conventional variable valve timing mechanism, there is a great restriction in increasing the maximum value of the intake / exhaust overlap amount, and the maximum value has to be set to about 40 ° crank angle. Therefore, effects such as reduction of NO _X , reduction of HC, and improvement of fuel efficiency in the middle and high rotation range could not be sufficiently exhibited.

An object of the present invention is to make it possible to set the maximum value of the intake / exhaust overlap amount to a large value while securing idle stability.
NO _X and H at least at high load in medium load condition
An object of the present invention is to provide an engine intake / exhaust control device capable of reducing C and improving fuel efficiency.

[Means for solving the problem]

An engine intake / exhaust control device according to claim 1, wherein the variable valve capable of changing the valve timing of the exhaust valve is provided in an engine having an intake control valve provided in each cylinder independent intake passage and closed and controlled in an idle state. A timing mechanism, operating state detecting means for detecting the number of revolutions and load of the engine, and an output of the operating state detecting means, the intake / exhaust overlap amount being maximized at least in a middle load state in a high speed region. Control means for controlling the variable valve timing mechanism so that the crank angle from the intake valve opening to the top dead center is the crank angle from the top dead center to the exhaust valve closing in the idle state where the intake and exhaust overlap amount is minimized. The valve timing is set to be at least 10 ° larger than the valve timing. According to a second aspect of the present invention, in the first aspect of the invention, the variable valve timing mechanism is configured to change a phase of the exhaust valve camshaft at one end of the exhaust valve camshaft. It is characterized by the following.

According to a third aspect of the present invention, there is provided the intake / exhaust control device for an engine according to the second aspect, wherein the variable valve timing mechanism comprises:
It is characterized in that the phase of the exhaust valve camshaft can be changed continuously.

[Action]

In the intake / exhaust control apparatus for an engine according to the present invention, the operation of the intake control valve, which is provided in each cylinder independent intake passage and is closed and controlled in the idle state, is set by setting the intake valve opening timing to be much earlier. The intake / exhaust overlap amount in the state is set to be large, so that the maximum value of the intake / exhaust overlap amount can be set significantly large without expanding the variable width of the intake / exhaust overlap amount of the variable valve timing mechanism. did.

That is, in the idle state, the intake control valve is closed, but the intake pressure on the downstream side of the intake control valve exhibits a behavior different from that of the throttle valve downstream boost negative pressure that is common to all cylinders. When the intake stroke is other than the intake stroke, the intake of approximately atmospheric pressure flowing from the gap between the closed intake control valves is accumulated in the independent intake passage portion between the intake control valves (ie, the intake negative pressure is not applied). Therefore, even if the intake valve is opened early and the amount of intake and exhaust overlap increases, exhaust gas does not flow back from the exhaust system into the combustion chamber, and the amount of residual gas remaining in the combustion chamber due to the intake and exhaust overlap is extremely small. It becomes very small. Therefore, the combustion stability is not impaired by the residual gas, and the idle stability does not decrease.

Here, as the variable valve timing mechanism, one that changes the valve timing of the exhaust valve is provided, so that a large change in the intake performance can be prevented, and the response of the residual gas amount to the change in the intake / exhaust overlap amount is also reduced. It is advantageous.
And since the intake valve opening timing has been greatly advanced,
Since the intake valve opening period becomes longer, the charging efficiency can be greatly increased.

Since the crank angle from the intake valve opening to the top dead center is set to be at least 10 ° larger than the crank angle from the top dead center to the exhaust valve closing in the idle state, the intake / exhaust overlap during idling as described above. The maximum value of the intake / exhaust overlap amount can be significantly increased without increasing the amount and the variable width of the variable valve timing mechanism without particularly increasing.

Since the intake / exhaust overlap amount is maximized at least in the middle load state in the high speed range via the control means, remarkable effects such as reduction of NO _X and HC, improvement of fuel consumption and improvement of torque characteristics can be obtained. . In the intake / exhaust control device for an engine according to the second aspect, the variable valve timing mechanism is configured to change the phase of the exhaust valve camshaft at one end of the exhaust valve camshaft. Excellent reliability.

In the intake / exhaust control apparatus for an engine according to the third aspect, the variable valve timing mechanism is configured to be able to continuously change the phase of the exhaust valve camshaft.
By appropriately setting the intake / exhaust overlap amount in accordance with the operating state of the engine, NO
_X reduction, HC reduction, improvement of fuel efficiency and improvement of torque characteristics can be achieved.

〔The invention's effect〕

According to the engine intake / exhaust control device according to claim 1,
As described in detail in the above section, the intake / exhaust overlap amount during idling can be set large while ensuring combustion stability during idling, thereby increasing the variable width of the variable valve timing mechanism. Without doing this, the maximum value of the intake / exhaust overlap amount can be significantly increased.

Therefore, by setting a sufficiently large intake and exhaust overlap amount at least in a medium load state in a high rotation range,
Significant effects such as reduction of NO _X and HC, improvement of fuel efficiency and improvement of torque characteristics can be obtained.

In addition, since the intake valve opening timing is remarkably advanced, the suction period is prolonged, and the charging efficiency can be greatly increased. According to the intake / exhaust control device for an engine of the second aspect, the structure of the variable valve timing mechanism is simplified and the reliability is excellent.

According to the intake and exhaust control device according to claim 3 of the engine, by appropriately setting the intake and exhaust overlap amount in accordance with the operating state of the engine, NO _X reduction over the entire operating conditions, HC reduction, fuel consumption And the torque characteristics can be improved.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

This embodiment is an example in which the present invention is applied to an intake / exhaust control device of a V-type six-cylinder engine with a mechanical supercharger for an automobile.

As shown in FIG. 1, the left bank 1A and the right bank 1B of the engine E are each provided with three cylinders 2, and each cylinder 2 is provided with two intake valves 3 and two exhaust valves 4, bank
An intake camshaft 5 for driving the intake valves 3 of 1A and 1B and an exhaust camshaft 6 for driving the exhaust valve 4 are provided. Pulleys 7 and 8 of these four camshafts 5 and 6 are connected via a timing belt. And are linked to the crankshaft.

The intake passage 9 includes a common intake passage 10 and this common intake passage
A left bank intake passage 11A and a right bank intake passage 11B branching left and right from 10, and an independent intake passage branching from the left bank intake passage 11A to an intake port of each cylinder 2 of the left bank 1A.
12 and each cylinder 2 of the right bank 1B from the right bank intake passage 11B
An independent intake passage 12 branches to an intake port of the common intake passage 10, and an air cleaner 13 and an air flow meter 14 are provided in the common intake passage 10.
And a mechanical supercharging machine 15 driven by a crankshaft, a throttle valve 16 is provided in the left and right bank intake passages 11A and 11B, and the left and right throttle valves 16 are connected to an accelerator pedal. .

An intake control valve 17 is provided in each independent intake passage 12, and the three intake control valves 17 of the left bank 1A and the three intake control valves 17 of the right bank 1B are fixed to a common support shaft 18, respectively. Opening / closing is controlled by rotating the support shaft 18. The control valves 20 and 21 for variable intake are used to enhance the intake charging efficiency by a resonance effect.The control valve 20 is used in a predetermined low rotation range and the control valve 21 is used in a predetermined high rotation range by an actuator (not shown). It is being opened.

A left bank exhaust passage 23A extending from the exhaust manifold 22A of the left bank 1A and a right bank exhaust passage 23B extending from the exhaust manifold 22B of the right bank 1B are connected to a combined exhaust pipe 24.

The valve timing changing mechanism 30 for changing the valve timing of the exhaust valve 4 of each bank 1A, 1B is provided by the exhaust camshaft 6.
Is interposed between the shaft end and the pulley 8. Since the left and right valve timing changing mechanisms 30 have the same structure,
The one in the left bank 1A will be described.

As shown in FIGS. 2 and 3, the valve timing changing mechanism 30 has a general structure, which will be briefly described.

A spacer 6a is fixed to the end of the exhaust camshaft 6, and the pulley 8 outside the spacer 6a is slidably in contact with the outer periphery of the distal end of the spacer 6a at the tip of the boss 32, and the base end of the boss 32 is used for exhaust. The cam shaft 6 is fixed to a rotatable connecting member 33. The connecting member 33 is rotatably supported by a bearing portion of a cylinder head, and a first gear 27 is spline-coupled to the other end of the connecting member 33. The second gear 28 is meshed and connected.

An annular piston 34 is incorporated between the boss 32 of the pulley 8 and the spacer 6a, and the piston 34 has a structure divided into two parts in the axial direction, and both parts are fixed to each other by a plurality of pins. Helical splines are formed on the inner and outer surfaces of the piston 34 in opposite directions. These helical splines are formed on the outer periphery of the spacer 6a and the helical splines.
Are engaged with the helical splines on the inner periphery of the boss portion 32, respectively. The piston 34 is urged toward the distal end by a spring 35.

An oil passage 36 is formed in the exhaust camshaft 6, and the spacer 6a is fixed to the exhaust camshaft 6 by a fixing bolt 38 via a stopper member 37, and the fixing bolt 38 has a through hole 39 communicating with the oil passage 36. A pressure chamber 40 for guiding the oil pressure from the oil passage 36 is provided at the tip of the boss 32 of the pulley 8.

The other end of the exhaust camshaft 6 is rotatably supported by a bearing portion of a cylinder head, and an end of the pivot support hole 41 is closed by a plug 42.

As shown in FIGS. 2 and 3, in order to supply and discharge oil pressure to and from the oil passage 36, a switching valve 43 which is switched by the overlap switching solenoid 31 is incorporated in the cylinder head. As shown, when the solenoid 31 is OFF, the switching valve 43 is in the exhaust position and the oil passage 36 is connected to the drain passage 44. When the solenoid 31 is ON, the switching valve 43 is in the supply position and the oil passage 36 is in the hydraulic supply passage 45 ( Oil gallery). Pressurized oil is supplied to the hydraulic supply path 45 from a lubricating oil pump driven by a crankshaft.

When the switching valve 43 is switched to the supply position via the switching solenoid 31, hydraulic pressure is supplied from the oil passage 36 to the pressure chamber 40, compressing the spring 35 and moving the piston 34 in the axial direction. Spacer through spline
Since the pulley 6a and the pulley 8 rotate relatively, the relative phase between the exhaust camshaft 6 integrated with the spacer 6a and the pulley 8 changes.

As described later, in the large overlap region, the oil pressure is supplied to the oil passage 36, so that the exhaust valve closing timing shifts to the lag side as shown by the dotted line in FIG. 4, and the intake valve opening timing does not change. In addition, the amount of overlap between intake and exhaust becomes large.
On the other hand, in the small overlap region, the oil pressure in the oil passage 36 is discharged, and the piston 34 returns with the elastic force of the spring 35, so that the overlap amount decreases as indicated by the solid line.

Here, as shown in FIG. 4, the crank angle θ _I from the opening of the intake valve to the top dead center is set to, for example, 30 °, and the exhaust angle from the top dead center when the intake / exhaust overlap amount is “small”. The crank angle θ _E1 until the valve is closed is set to, for example, 10 °, and the crank angle θ _E2 from the top dead center to the exhaust valve closing when the intake / exhaust overlap amount is set to `` large '' is set to, for example, 30 °. I have.

As described later, in order to maximize the intake / exhaust overlap amount (θ _I + θ _E2 ) in the high rotation range, the intake valve opening timing angle θ _I is at least 10 ° larger than the exhaust valve closing timing angle θ _E1. Is set to the valve timing.

Control unit for controlling the engine E
25, an air flow meter 14, a throttle opening sensor (not shown) for detecting the opening of the throttle valve 16, an idle switch 26, a crank angle sensor 29 provided in a distributor, and a reference crank angle sensor 3.
0, and other signals from various sensors and switches (not shown) are input to the control unit 25, and the control unit 25 injects fuel into the ignition unit and the intake port of each cylinder 2 (not shown). ), A drive signal is output to the switching solenoid 31 and the like.

The control unit 25 includes a microcomputer having an input / output interface, a CPU (central processing unit), a ROM (read only memory) and a RAM (random access memory), and an intake air amount signal from the air flow meter 14. A / D converter for AD conversion, A / D for AD conversion of throttle opening signal from throttle valve opening sensor
It is provided with a converter, a drive circuit for an injector, a drive circuit for an ignition unit, a drive circuit for a switching solenoid 31, and the like.

In the ROM, a control program for ignition timing control, a control program for fuel injection control, a control program for valve timing switching control for switching and controlling the intake / exhaust overlap amount via a switching solenoid 31, which will be described later, and a map attached thereto, A control program for closing and controlling the intake control valve 17 via the actuator 19 in the idle state and various other control programs are input and stored in advance.

FIG. 5 shows a small overlap region in which the intake / exhaust overlap amount (which is abbreviated as O / L in the figure) in the operation region of the engine E is set to be small, and an overlap region in which the intake / exhaust overlap amount is set to be large. This indicates a large area, which is previously input and stored in the ROM as a map using the engine speed and the load as parameters. Note that the small overlap region and the large overlap region are separated by the solid line A, but the present invention is not limited to this and may be separated by the chain line B.

Since the control for switching the intake / exhaust overlap amount is a simple control, a description will be given without using a flowchart. In the following description, the engine speed is determined using the crank angle signal from the crank angle sensor 29 over the entire period during which the engine E is operating. , And
The load is calculated from the amount of intake air read from the air flow meter 14 and the engine speed, and the operating state of the engine E is determined based on the engine speed and the load. Control is performed so that the switching solenoids 31 of the left and right banks 1A and 1B are turned off when in the overlap small area, and the switching solenoids 31 of the left and right banks 1A and 1B are controlled when the overlap is in the large overlap area. Control to turn on.

On the other hand, regarding the control for the intake control valve 17, it is determined whether or not the engine is in the idle state based on signals from the idle switch 26, the neutral switch of the transmission, and the like. When the idle state is reached, the actuators of the left and right banks 1A and 1B are actuated. 19
The intake control valve 17 is switched from open to closed via. However, even if the intake control valve 17 is switched to the closed state, the intake air required for the idling operation flows.

Thus, when the operating state is in the small overlap region, the intake and exhaust overlap amount is controlled to be small, and when the operating state is in the large overlap region, the intake and exhaust overlap amount is controlled to be large.

Next, the operation of the engine intake / exhaust control device will be described.

The intake control valve 17 is basically provided for facilitating idle adjustment of the throttle valve 16 and ensuring idle stability, and is closed only during an idle state.
Otherwise, it is controlled to be fully open.

When the intake control valve 17 is provided, the gas pressure in the intake port of each independent intake passage 12 (gas pressure between the intake control valve 17 and the intake valve 3) is as shown in FIG. That is, when the intake valve 3 is opened, a large intake negative pressure acts.
Is in the closed state, the intake air flows through the intake control valve 17, and the pressure becomes approximately atmospheric pressure. This is the same at the time of idling. Even when the intake control valve 17 is in the closed state, there is a gap enough to allow only the intake air for idling to flow, so that the intake air flows into approximately the atmospheric pressure. As described above, the gas pressure in the intake port before the intake valve 3 is opened is substantially the atmospheric pressure. Therefore, even if the intake valve 3 is opened early, burned gas does not flow into the intake port.
Since the opening timing of the intake valve 3 is advanced, the residual gas amount in the combustion chamber does not increase during idling. Therefore, the intake / exhaust overlap amount (θ _I +
Even if θ _E1 ) is set to a value as large as about 40 °, the residual gas does not increase and the combustion stability is not impaired.

Further, the valve timing changing mechanism 30 is connected to the exhaust camshaft 6.
, The opening timing of the intake valve is fixed, so that a large change in the intake performance can be prevented, and the responsiveness of the residual gas amount to a change in the intake / exhaust overlap amount can be ensured.

FIGS. 8 to 10 show the effect of the intake and exhaust overlap amount on the engine performance. As the intake and exhaust overlap amount increases, the amount of burned gas remaining in the combustion chamber increases and the combustibility increases. since is suppressed, NO _X concentrations higher the irrespective intake and exhaust amount of overlap of the number of engine circuit is reduced. In addition, regarding the full opening torque, the exhausted HC concentration, and the fuel efficiency, it is desirable to increase the intake / exhaust overlap amount in accordance with the increase in the engine speed or the load. However, in the low rotation range and low load conditions, the new aeration amount is small, the combustion stability is low, the suction negative pressure is large, and the exhaust gas backflow increases, so the combustion stability decreases as the intake / exhaust overlap amount increases. I do.

Here, as shown in FIG. 5, since the intake / exhaust overlap amount is set to be small in the low rotation speed range, combustion stability including idle stability during idling can be ensured.

Fully open torque is set larger the intake and exhaust overlap amount in the medium speed region, NO _X concentration can improve the HC concentration and fuel consumption.

In the high rotation region, aims to improve such a low intake and exhaust overlap amount set large to fully open the torque since the combustion stability sufficient even when the load state, NO _X, HC, intake and exhaust during medium and high load conditions By setting the overlap amount large, it is possible to improve the full opening torque, NO _X , HC and the like as in the low load state. Here, when the intake performance and the scavenging performance of the engine E are high, the intake / exhaust overlap amount may be set to be large when the engine E is in a high load state in a middle to high rotation range as shown in FIG. When the scavenging performance is low, it is desirable to set the intake / exhaust overlap amount small in a high load state in the middle and high rotation range to prevent the output from lowering.
However, at least at the time of a medium load state in the high rotation range, the intake / exhaust overlap amount is set to the maximum in order to maximize the internal EGR action.

Since it is desirable to increase the intake / exhaust overlap amount in accordance with the increase in the load, the overlap small region and the overlap large region may be divided by a straight line C as shown in FIG. The non-supercharged area where the supercharger 15 is not operated (the area inside the broken line D) is defined as a small overlap area, and the supercharged area where the supercharger 15 is operated (the area outside the broken line D) is defined as a large overlap area. Is also good. That is,
When supercharging, the sweeping action by supercharging intake is strengthened,
Since the residual gas amount is reduced, it is reasonable to increase the intake and exhaust overlap amount in the supercharging region.

<First Alternative Embodiment> In this embodiment, not only the exhaust camshaft 6 but also the intake camshaft 5 is provided with the valve timing changing mechanism 30 and the oil passage 3.
6. The same components as the switching valve 43 and the switching solenoid 31 are incorporated, and the valve timing of the exhaust valve 4 and the valve timing of the intake valve 3 can be switched as shown in FIG. Depending on the combination of the valve timing of the valve 4, the intake / exhaust overlap amount is "small", "medium",
It is configured to be able to switch to three types of “large”.

That is, in FIG. 11, for example, θ _I1 ≒ 20 °, θ _I2 ≒ 30
°, θ _E1 = 10 °, θ _E2 ≒ 30 °, overlap amount “small” = (θ _I1 + θ _E1 ), overlap amount “medium”
= (Θ _I2 + θ _E1 ) or (θ _I1 + θ _E2 ), and the overlap amount “large” is set as (θ _I2 + θ _E2 ). However, since there are four combinations at the valve timing shown in FIG. 11, it is possible to switch the overlap amount to four stages.

Fig. 12 shows the intake / exhaust overlap amount "small", "medium" and "large"
Shows an overlapping small area, a middle overlapping area, and a large overlapping area, respectively, corresponding to
It is input and stored in the ROM in advance in the form of a map.

It should be noted that the overlapped area and the large overlap area are not separated by a straight line E, and in the case of an engine having insufficient intake performance and scavenging performance, a broken line F is used to prevent a decrease in output during a high load condition in a high rotation range. It is also possible to classify.

As in this embodiment, the intake / exhaust overlap amount is switched between small, medium and large for each area shown in FIG. 12, so that the engine performance can be further improved. Since the configuration other than the above is the same as that of the above-described embodiment, the description is omitted.

Note that the overlap amounts "small", "medium" and "large"
It could be as large as 40 °, 60 °, 80 °, etc.

<Second Alternative Embodiment> In this embodiment, as shown in FIG. 13, the switching solenoid 31, the switching valve 43, and the plug 42 are removed, and the oil passage 36 is provided at the end of the exhaust camshaft 6. Relief valve facing the end of
A relief valve 50 including a relief solenoid 51 for controlling the opening and closing of the relief valve element 51 is provided. When the relief valve 50 is opened, part of the oil pressure in the oil passage 36 flows from the end of the pivot hole 41 to the drain passage 44, so that the oil pressure in the pressure chamber 40 decreases.

The hydraulic pressure supply passage 45 is formed in the pivot portion A of the cylinder head, is connected to the oil gallery of the cylinder head 2, and is supplied with pressurized oil from the oil gallery. The oil pressure supply passage 45 communicates with the oil passage 45 through an annular groove 45a and a through hole 45b of the exhaust camshaft.

Further, a pressure sensor 46 for detecting the oil pressure in the oil gallery, that is, the oil pressure in the pressure chamber 40 is provided. A detection signal of the pressure sensor 46 is supplied to the control unit 25, and a drive pulse is output from the control unit 25 to the linear solenoid 52. As a result, the oil pressure in the pressure chamber 40 can be freely and continuously feedback-controlled within a range not more than the oil pressure in the oil gallery.

The valve timing changing mechanism 30 has basically the same configuration as that of the embodiment described above, and the same members are denoted by the same reference numerals and description thereof is omitted, but the maximum change width of the valve timing of the exhaust valve 4 is set to be large. ing. Since the oil pressure in the pressure chamber 40 can be controlled steplessly as described above, the valve timing of the exhaust valve 6 can also be controlled steplessly.

Further, as shown in FIG. 14, the intake / exhaust overlap amount is set so as to increase as the engine speed increases, and to be larger in the medium load region than in the small load and high load regions. It is input and stored in the ROM in advance in the form of a map in which the entire operation area is divided into several tens of small areas.
Note that the plurality of curves in FIG. 14 show equal overlap amount lines in which the intake and exhaust overlap amounts are equal.

Therefore, the operating state of the engine E is obtained, and the intake / exhaust overlap amount corresponding to the operating state is read from the map,
The pressure sensor 46 is set so that the intake and exhaust overlap amount
The pressure in the pressure chamber 40 is controlled via the linear solenoid 52 and the linear solenoid 52.

As in this embodiment, by setting a large intake and exhaust overlap amount in response to the engine rotational speed is increased, NO _X reduction over the entire operating conditions, HC reduction, improvement and torque characteristics of the fuel Can be improved. However, in order to prevent a decrease in output in a high-load region, a limit may be imposed on the intake / exhaust overlap amount in the high-load region.

In consideration of the fact that the supply oil pressure is low when the engine speed is low, measures such as increasing the pressure receiving area of the piston 34 or providing an oil pressure accumulator to back up the oil pressure when the oil pressure is low may be taken. . Alternatively, a small-sized electric oil pump may be provided, and a predetermined oil pressure may be supplied to the pressure chamber 40 from the electric oil pump instead of the oil gallery.

Instead of the valve timing changing mechanism of the above embodiment, a valve timing changing mechanism of the mechanism described in Japanese Patent Application Laid-Open No. 1-247724 or another existing valve timing changing mechanism may be used.

Although the above embodiment has been described with reference to an engine with a supercharger, it goes without saying that the present invention can be applied to a naturally-aspirated engine without a supercharger.

[Brief description of the drawings]

1 shows an embodiment of the present invention, FIG. 1 is an overall configuration diagram of an engine and its intake / exhaust control device, FIG. 2 is a sectional view of a valve timing changing mechanism, FIG. 3 is a sectional view of a switching valve,
FIG. 4 is an explanatory diagram of valve timing, FIGS. 5 and 6 are explanatory diagrams of areas of large and small overlap, respectively, FIG. 7 is a time chart of gas pressure in each intake port, and FIG. Figure, FIG. 9 is the case of constant load NO _X concentration and HC
Diagram of concentration, Fig. 10 in the case of a constant rotational speed NO _X concentration and H
Diagram of C concentration, FIG. 11 is an explanatory diagram of valve timing according to the first alternative embodiment, FIG. 12 is an explanatory diagram of an overlap large, medium and small area according to the first alternative embodiment, and FIG. FIG. 14 is a diagram corresponding to FIG. 2 according to another embodiment, and FIG. 14 is an explanatory diagram of an overlap change region according to the second embodiment. 3 ... intake valve, 4 ... exhaust valve, 12 ... independent intake passage, 17
... intake control valve, 19 ... actuator, 25 ... control unit, 29 ... crank angle sensor, 30 ... valve timing change mechanism, 31 ... switching solenoid.

Continuation of front page (56) References JP-A-61-23827 (JP, A) JP-A-62-294719 (JP, A) JP-A-1-224416 (JP, A) JP-A-3-138443 (JP) JP-A-63-195325 (JP, A) JP-A-62-191636 (JP, A) JP-A-2-1199641 (JP, A) JP-A-3-179131 (JP, A) 62-76237 (JP, U) Actually open 62-28033 (JP, U)

Claims (3)

(57) [Claims] 1. An engine provided with an intake control valve provided in each cylinder independent intake passage and controlled to be closed when idling, a variable valve timing mechanism capable of changing a valve timing of an exhaust valve, and an engine speed. Operating state detecting means for detecting the load and the load, and receiving the output of the operating state detecting means, and controlling the variable valve timing mechanism so that the intake and exhaust overlap amount is maximized at least in a medium load state in a high speed range. In the idle state where the intake and exhaust overlap amount is minimized, the crank angle from the intake valve opening to the top dead center is at least 10 ° larger than the crank angle from the top dead center to the exhaust valve closing An intake and exhaust control device for an engine, wherein the valve timing is set as described above. 2. The intake / exhaust control of an engine according to claim 1, wherein the variable valve timing mechanism is configured to change a phase of the exhaust valve camshaft at one end of the exhaust valve camshaft. apparatus. 3. The intake / exhaust control device for an engine according to claim 2, wherein the variable valve timing mechanism is configured to be able to continuously change the phase of an exhaust valve camshaft.