JP2000045802A - Valve timing control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the engine power from remarkably decreasing in an engine speed at which positive pressure-reflected wave comes to an exhaust valve even when the amount of change required for a target valve closing timing increases exceeding a specified value. SOLUTION: A valve timing control device for internal combustion engines is provided with a variable valve timing mechanism for making at least the valve closing timing of an exhaust valve and the valve opening timing of an intake valve variable; a first control means (a first map A) for controlling the valve closing timing of the exhaust valve by the variable valve timing mechanism based on target valve closing timings set for every engine speed for early closing the exhaust valve at a specified speed at which positive pressure-reflected wave causing exhaust pulsation comes to the exhaust valve; and a second control means (a fourth map D) for changing the valve opening timing of the intake valve in a direction opposite to the change direction of the valve closing timing of the exhaust valve by the valve timing mechanism, when the required amount of change for a target valve closing timing increases exceeding a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a valve timing control device for an internal combustion engine.

[0002]

2. Description of the Related Art Exhaust gas discharge causes exhaust pulsation in an exhaust passage, and negative pressure reflected waves and positive pressure reflected waves arrive at an exhaust valve at different specific engine speeds. If a negative pressure reflected wave arrives at the exhaust valve when the exhaust valve and the intake valve both open at the time of valve overlap, the intake filling efficiency can be improved. When it reaches the exhaust valve, the intake charging efficiency is reduced.

Accordingly, Japanese Patent Application Laid-Open No. Hei 9-10072 discloses a technique for preventing a reduction in intake air charging efficiency.
The variable valve timing mechanism closes the exhaust valve based on the target valve closing timing set for each engine speed so that the exhaust valve closes early at the specific engine speed at which the positive pressure reflected wave arrives at the exhaust valve. The valve timing is controlled.

[0004]

Generally, the variable valve timing mechanism mechanically changes the valve timing. Therefore, when the required change amount to the target valve closing timing is small, the actual exhaust valve is controlled. Can be satisfactorily matched with the target valve closing timing. However, for example, when the engine speed suddenly changes to a specific engine speed at which the positive pressure reflected wave arrives at the exhaust valve, the required change amount to the target valve closing timing becomes considerably large, so that a response delay occurs. Due to this, the actual closing timing of the exhaust valve greatly deviates from the target closing timing, and the positive pressure reflected wave of exhaust pulsation arrives at the exhaust valve that is opening, reducing the intake charge efficiency and greatly reducing the engine output. I do.

Accordingly, an object of the present invention is to provide a large engine output even when a required change amount to a target valve closing timing exceeds a predetermined value at an engine speed at which a positive pressure reflected wave arrives at an exhaust valve. An object of the present invention is to provide a valve timing control device for an internal combustion engine that can prevent a decrease.

[0006]

SUMMARY OF THE INVENTION A valve timing control apparatus for an internal combustion engine according to the present invention includes a variable valve timing mechanism for varying at least the closing timing of an exhaust valve and the opening timing of an intake valve, and a positive pressure of exhaust pulsation. At a specific engine speed at which a reflected wave arrives at the exhaust valve, the exhaust valve is closed by the variable valve timing mechanism based on a target valve closing timing set for each engine speed in order to close the exhaust valve early. First control means for controlling the closing timing of the exhaust valve, and when the required change amount to the target closing timing exceeds a predetermined value, the valve timing mechanism sets the opening timing of the intake valve to the exhaust valve. A second control unit that changes the valve closing timing in a direction opposite to the changing direction.

In the valve timing control apparatus for an internal combustion engine according to the present invention, in the valve timing control apparatus for an internal combustion engine according to the first aspect of the present invention, the second control means may include a desired valve over set for each engine speed. The valve opening timing of the intake valve is changed so as to maintain the lap period.

The valve timing control device for an internal combustion engine according to the present invention is the valve timing control device for an internal combustion engine according to claim 1 or 2, wherein the second control means is configured to control the engine speed to the specific engine speed. The valve opening timing of the intake valve is changed when the rotation speed changes within a predetermined rotation speed range in the vicinity.

[0009]

FIG. 1 is a schematic diagram of an internal combustion engine equipped with a valve timing control device according to the present invention. In the figure, 1 is a piston, and 2 is a spark plug. An exhaust passage 4 communicates with the cylinder via an exhaust valve 3, and an intake passage 6 communicates with the cylinder via an intake valve 5.

A camshaft 11 for the intake valve 5 is connected to a crankshaft via a belt or the like by a pulley 11a provided at an end thereof, and the pulley 11a is connected to an end of a camshaft 12 for the exhaust valve 3. Are connected to each other via a belt or the like. Thereby, both camshafts 11 and
Reference numeral 12 is driven to rotate, and the intake valve 5 and the exhaust valve 3 are opened and closed.

The camshaft 11 for the intake valve 5 and the camshaft 12 for the exhaust valve 3 are provided with generally known variable valve timing mechanisms. This is for rotating the camshafts 11 and 12 and the pulleys 11a and 12a relative to each other. For example, they are connected via an intermediate gear having helical teeth as external teeth, and this intermediate gear is hydraulically or electromagnetically driven. The relative rotation described above is realized by moving in the axial direction by utilizing the above-described method, whereby the valve timings of the intake valve 5 and the exhaust valve 3 can be changed steplessly.

Reference numeral 20 denotes a control device for controlling the closing timing of the intake valve 5 and the opening timing of the exhaust valve 3 using the variable valve timing mechanism. A rotation sensor 21 and the like for detecting the rotation angle are connected.

A solid line A in FIG. 2 is a first map showing the target closing timing of the exhaust valve 3 for each engine speed, and a solid line B is a second map showing the target opening timing of the intake valve 5. The control device 20 uses the variable valve timing mechanism based on the engine speed detected by the rotation sensor 21 as the first control means, and performs the exhaust control as shown in the first map A and the second map B in FIG. The closing timing of the valve 3 and the opening timing of the intake valve 5 are controlled. In this control, when the closing timing of the exhaust valve 3 is changed to use the above-described variable valve timing mechanism, the opening timing of the exhaust valve 3 is also changed accordingly, and the opening timing of the intake valve 5 is changed. Is changed, the closing timing of the intake valve 5 changes accordingly.

A first map A and a second map B shown in FIG.
In the engine idle region, the opening timing of the intake valve 5 and the closing timing of the exhaust valve 3 are set near the top dead center, and the valve overlap period in which both the intake valve 5 and the exhaust valve 3 are open is compared. Have been made smaller. When the engine is idle, if the exhaust gas flows back to the engine intake system, the engine may stop due to combustion deterioration. Therefore, the valve overlap period is set relatively small, and the exhaust gas backflow is reliably prevented. .

On the other hand, in the low engine speed region except when the engine is idling, the opening timing of the intake valve 5 is largely advanced from the top dead center, and the closing timing of the exhaust valve 3 is generally the top dead center. The valve is greatly retarded from the point, and the valve overlap period is made relatively long. In this region, if the closing timing of the intake valve 5 is greatly retarded from the bottom dead center, the intake air drawn into the cylinder is discharged to the intake system and the intake charging efficiency is reduced, so that the intake valve 5 is closed. The timing is near the bottom dead center, and accordingly, the opening timing of the intake valve 5 is greatly advanced from the top dead center. Further, in this region, since the exhaust stroke time is long, exhaust gas can be discharged relatively satisfactorily without sacrificing the engine output and greatly opening the exhaust valve 3 from the bottom dead center. It is. As a result, the valve opening timing of the exhaust valve 3 is set near the bottom dead center, and accordingly, the valve closing timing of the exhaust valve 3 is greatly delayed from the top dead center.

As a result, the valve overlap period becomes relatively long. However, in the engine exhaust system of the present embodiment, the first specific engine speed N included in the engine low speed region is included.
In FIG. 1, the negative pressure reflected wave of the exhaust pulsation arrives at the exhaust valve 3, and the exhaust gas is more sufficiently discharged by this large valve overlap period.
The intake charging efficiency is improved, and the engine output can be increased.

In the high engine speed region, the opening timing of the intake valve 5 and the closing timing of the exhaust valve 3 are generally set near the top dead center, and the valve overlap period is relatively short. In this region, if the closing timing of the intake valve 5 is greatly delayed from the bottom dead center, the intake charging efficiency can be increased by the inertia of the intake air. The intake valve 5 is retarded, and accordingly, the opening timing of the intake valve 5 is set near the top dead center. In this area,
Since the exhaust stroke time is short, it is impossible to exhaust the exhaust gas sufficiently unless the valve opening timing of the exhaust valve 3 is advanced from the bottom dead center. As a result, the opening timing of the exhaust valve 3 is greatly advanced from the bottom dead center, and accordingly, the closing timing of the exhaust valve 3 is set near the top dead center.

In the low engine speed region, in the engine exhaust system of the present embodiment, the positive pressure reflected wave of the exhaust pulsation arrives at the exhaust valve 3 at the second specific engine speed N2. Accordingly, in the vicinity of the engine speed N2,
The closing timing of the exhaust valve 3 is advanced to near the top dead center. In this way, it is intended to prevent a problem that a large amount of exhaust gas flows back into the engine intake system through the cylinder, thereby greatly reducing the intake charging efficiency and greatly reducing the engine output.

Generally, a first specific engine speed N1 at which a negative pressure reflected wave of exhaust pulsation arrives at the exhaust valve 3 and a second specific engine speed N1 at which a positive pressure reflected wave of exhaust pulsation arrives at the exhaust valve 3 N2
Is relatively close, so that the target closing timing of the exhaust valve 3 is surely largely changed in the range between these two engine speeds N1 and N2 regardless of the present embodiment. In the present embodiment, in the low engine speed region including these specific engine speeds N1 and N2, as described above, it is preferable that the valve opening timing of the exhaust valve 3 is set near the bottom dead center. Accordingly, when the engine speed reaches the third specific engine speed N3 immediately after exceeding the second specific engine speed N2, the target valve closing timing is greatly retarded from the top dead center. Thus, in the present embodiment, the target valve closing timing of the exhaust valve 3 greatly changes within the predetermined rotational speed range R from the first specific engine rotational speed N1 to the third specific engine rotational speed N3. .

If the change in the engine speed is gradual, the exhaust valve 3 is controlled by the aforementioned variable valve timing mechanism according to the first map A in FIG.
Can be controlled to the target valve closing timing. The solid line in FIG. 3 shows the engine output with respect to the engine speed when the target closing timing of the exhaust valve 3 and the target opening timing of the intake valve 5 are realized according to the first map A and the second map B in FIG. This is a graph, and thus a high engine output can be obtained as a whole.

However, when the change in the engine speed is rapid, the closing timing of the exhaust valve 3 does not coincide with the target closing timing due to a response delay within the predetermined rotation speed range R.
It can only be changed as shown by the dotted line in FIG. As a result, the engine output is reduced by the above-mentioned positive pressure reflected wave, as shown by the one-dot chain line in FIG.

The valve timing control device for an internal combustion engine according to this embodiment controls the variable valve timing mechanism in accordance with the flowchart shown in FIG. 4 in order to prevent such a decrease in engine output.

First, at step 101, the current engine speed N is read by the rotation sensor 21. next,
In step 102, the target closing timing Tc of the exhaust valve 3 and the target opening timing To of the intake valve 5 at the engine speed N are determined based on the first map A and the second map B in FIG. Next, at step 103, the engine speed N
From the first specific engine speed N1 to the third specific engine speed N3
Is determined to be within the predetermined rotation speed range R.

When this determination is denied, that is, when the current engine speed N is out of the predetermined speed range R, the variable valve timing mechanism is used to control the engine speed N.
Can be sufficiently matched with the target closing timing Tc and the target opening timing To, even if the change of the exhaust valve 3 is abrupt, and the process proceeds to step 107. Target valve closing timing T determined in step 102
The variable valve timing mechanism is controlled based on c and the target valve opening timing To.

When the determination at step 103 is affirmative, the routine proceeds to step 104, where the required change amount ΔTc from the previous closing timing of the exhaust valve 3 to the target closing timing Tc is determined.
Is larger than a predetermined value K. When this determination is denied, the change in the engine speed is gradual even when the current engine speed N is within the predetermined speed range R, so that the variable valve timing mechanism described above is used as shown in the first map A in FIG. The closing timing of the exhaust valve 3 can be controlled,
Proceeding to step 107, the variable valve timing mechanism is controlled based on the target valve closing timing Tc and the target valve opening timing To determined in step 102.

On the other hand, when the determination in step 104 is affirmative, the second control means different from the above-described first control means is executed in step 105 based on the third map C shown by a dotted line in FIG. The target valve closing timing Tc 'at the engine speed N is determined based on the fourth map D shown by the dotted line in FIG.
o ′ is determined, and this is set as the target valve opening timing To. Next, the process proceeds to step 107, and steps 105 and 106 are performed.
The variable valve timing mechanism is controlled based on the target valve closing timing Tc and the target valve opening timing To determined in.

As described above, if the valve closing timing of the exhaust valve 3 is merely changed in accordance with the third map C in FIG. 2, the engine output decreases as shown by the dashed line in FIG. In the embodiment, at the same time, the opening timing of the intake valve 5 is changed according to the fourth map D in FIG. The fourth map D represents a valve overlap period for each engine speed determined by the closing timing of the exhaust valve in the first map A and the opening timing of the intake valve in the second map B.
The opening timing of the intake valve 5 is set so as to be maintained with respect to the closing timing of the exhaust valve in the third map C.

As a result, even when the change in the engine speed is abrupt within the predetermined speed range, the valve overlap period is maintained for each engine speed. Thus, for example,
The second specific engine speed N at which the negative pressure reflected wave arrives at the exhaust valve 3
When the engine speed changes suddenly to 2, the closing timing of the exhaust valve is not sufficiently advanced as shown in the third map C of FIG. 2, but the opening timing of the intake valve 5 is accordingly reduced. As shown in the fourth map D, the backflow of the exhaust gas to the engine intake system due to the negative pressure reflected wave can be reduced.

FIG. 5 is a graph showing a change in the engine output with respect to the closing timing of the exhaust valve 3 at the second specific engine speed N2, and the solid line indicates the target opening timing of the intake valve 5 in the second map of FIG. When the valve is opened at To1, the dotted line indicates that the intake valve 5 is set at 10 ° from the target valve opening timing To1 in the second map of FIG.
In the case of retarding, the chain line shows the case where the intake valve 5 is retarded by 20 ° from the target valve opening timing To1 in the second map of FIG. Tc1 in FIG. 5 corresponds to the target valve closing timing Tc1 in the first map in FIG. As shown by the solid line, when the valve closing period of the exhaust valve 3 is delayed by 20 ° (crank angle, hereinafter the same) from Tc1 when the opening timing of the intake valve 5 is To1, the engine output becomes P1 to P1.
2, the engine output becomes P1 if the valve opening timing of the intake valve 5 is simultaneously delayed by 20 ° from To1 to maintain the desired valve overlap period T at this time, as shown by the one-dot chain line. From P3 to P3.
Thus, when the positive pressure reflected wave arrives at the exhaust valve, the optimal exhaust valve closing timing Tc1 and the optimal intake valve opening timing T
If the optimal valve overlap period determined by o1 is maintained, even if the closing timing of the exhaust valve and the opening timing of the intake valve are shifted, a large decrease in engine output does not occur. Thus, according to the present embodiment, even when the change in the engine speed is abrupt within the predetermined speed range, as shown by the dotted line in FIG. 3, it is possible to prevent a large decrease in the engine output.

In the present embodiment, the target closing timing of the exhaust valve of the third map C in the predetermined rotation speed range R is determined by using the upper limit of the responsiveness of the variable valve timing mechanism. The target valve opening timing of the intake valve in the fourth map D is determined so as to maintain an optimal valve overlap period at each engine speed with respect to the target valve closing timing in the third map C. As a result, the target valve closing timing in the third map C is made as close as possible to the optimal target valve closing timing shown in the first map of FIG. 2, and a decrease in engine output can be minimized.

The target valve closing timing of the third map C and the target valve opening timing of the fourth map D in a predetermined rotation speed range are as follows:
The advance from the target valve closing timing Tc2 and the target valve opening timing To1 at the first specific engine speed N1 while maintaining the optimum valve overlap for each engine speed shown in the first map A and the second map B. The amount and the retard amount may be set to be equal. As a result, the required change amount of the exhaust valve and the required change amount of the intake valve in the predetermined rotational speed range become equal, and the required response of the variable valve timing mechanism can be reduced.

In this embodiment, when the required change amount of the exhaust valve to the target valve closing timing is larger than a predetermined value, the opening timing of the intake valve is adjusted so that the desired valve overlap period is realized. The change direction (advance or retard) of the valve closing timing is changed in the opposite direction (retard or advance).
In particular, when the positive pressure reflected wave arrives at the exhaust valve, even if the desired valve overlap period is not realized, if the valve opening timing of the intake valve is changed, the exhaust gas to the engine intake system can be compared with the conventional case. The backflow of gas can be reduced, and the decrease in engine output can be reduced.

In this embodiment, the opening timing of the intake valve is changed when the required change amount of the exhaust valve to the target closing timing is larger than a predetermined value. May be changed according to the condition. Further, the actual valve closing timing may be compared with the target valve closing timing, and when it is detected that a response delay has occurred in the variable valve timing mechanism, the valve opening timing of the intake valve may be changed.

The variable valve timing mechanism of the present embodiment uses an intermediate gear and, when the valve closing timing of the intake / exhaust valve is advanced, the valve opening timing is also advanced at the same time. Equipped with a fluid cylinder between the intake and exhaust valves,
A variable valve timing mechanism that allows the intake and exhaust valves to be opened and closed at any time by controlling the supply and discharge of fluid such as hydraulic oil to the fluid cylinder is used. Apart from the control of the valve opening timing described above, only the valve opening timing of the intake valve and the valve closing timing of the exhaust valve may be controlled in accordance with the above-described flowchart. In the present embodiment, the optimal valve overlap period for each engine speed is large in the low rotation region and small in the high rotation region, but this is not a limitation of the present invention.

[0035]

As described above, according to the valve timing control apparatus for an internal combustion engine according to the present invention, normally, the first control means uses the variable valve timing mechanism to set the closing timing of the exhaust valve to the target closing timing. The exhaust valve can be closed early at the engine speed at which the positive pressure reflected wave of the exhaust pulsation reaches the exhaust valve. Further, when the required change amount to the target valve closing time exceeds a predetermined value, the second control means causes the valve timing mechanism to change the opening timing of the intake valve to the changing direction of the closing timing of the exhaust valve. At the engine speed at which the positive pressure reflected wave of exhaust pulsation arrives at the exhaust valve due to the change in the reverse direction, the valve closing timing of the exhaust valve cannot be sufficiently advanced due to the response delay of the variable valve timing function. At the same time, by retarding the opening timing of the intake valve, the reverse flow rate of the exhaust gas to the intake system is reduced, and a significant decrease in engine output can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an internal combustion engine equipped with a valve timing control device according to the present invention.

FIG. 2 is a map showing a target closing timing of an exhaust valve and a target opening timing of an intake valve.

FIG. 3 is a graph showing engine output with respect to engine speed;

FIG. 4 is a flowchart for controlling a variable valve timing mechanism according to the present invention.

FIG. 5 is a graph showing a change in engine output with respect to a closing timing of an exhaust valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piston 2 ... Combustion chamber 3 ... Fuel injection nozzle 4 ... Exhaust valve 6 ... Intake valve 20 ... Control device

Claims (3)

[Claims] 1. A variable valve timing mechanism for varying at least the closing timing of an exhaust valve and the opening timing of an intake valve;
At a specific engine speed at which a positive pressure reflected wave of exhaust pulsation arrives at the exhaust valve, to close the exhaust valve early,
First control means for controlling the closing timing of the exhaust valve by the variable valve timing mechanism based on a target closing timing set for each engine speed; and a required change amount to the target closing timing is a predetermined value. Internal control means for changing the opening timing of the intake valve by the valve timing mechanism in a direction opposite to the direction in which the closing timing of the exhaust valve changes. Engine valve timing control device. 2. The system according to claim 1, wherein the second control means changes the valve opening timing of the intake valve so as to maintain a desired valve overlap period set for each engine speed. A valve timing control device for an internal combustion engine according to any one of the preceding claims. 3. The valve control apparatus according to claim 1, wherein the second control means changes the valve opening timing of the intake valve when the engine speed changes to a predetermined engine speed range near the specific engine speed. Or a valve timing control device for an internal combustion engine according to item 2.