JP2000230409A - Variable valve device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To positively rotate a tappet by offsetting a press position of a cam lobe from the center of the tappet. SOLUTION: A cam shaft 14 having a pair of can lobes 16 at the periphery thereof is relatively rotatably fitted over a drive shaft 12. A tappet 19 is interposed between each cam lobe 16 and an intake valve 18. Link functions 22, 28, 30 interconnecting the drive shaft 12 and the cam shaft 14 are provided with a variable mechanism 24 to vary a lift characteristic of the intake valves 18. With respect to the center of each tappet 19A, 19B, the axial center of each cam lobe 16A, 16B is axially offset toward a link connecting part where a rod-shaped link 30 and an axial end of the cam shaft 14 are interconnected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a variable valve operating device that can change the opening / closing timing and valve lift of an intake / exhaust valve (an intake valve or an exhaust valve) in accordance with the operating state of an internal combustion engine.

[0002]

2. Description of the Related Art In the field of internal combustion engines, intake and exhaust are required to improve fuel efficiency at low speed and low load, to ensure stable driving performance, and to secure sufficient output by improving intake charging efficiency at high speed and high load. Various variable valve operating devices have been proposed that change the valve opening / closing timing and the valve lift amount in accordance with the operating state of the engine.

As such a variable valve operating device, for example,
A drive shaft that rotates in synchronization with the engine and a camshaft that drives the intake and exhaust valves are linked by a link mechanism, and a variable mechanism that changes the lift characteristics of the intake and exhaust valves is linked to this link mechanism. Are described in JP-A-7-34820.

[0004] Briefly referring to FIG. 9, a camshaft 2 divided for each cylinder is rotatably fitted on the outer periphery of a drive shaft 1 which rotates in synchronization with the engine. A pair of cam lobes 3 are provided on the outer periphery of each cam shaft 2, and each cam lobe 3 comes into contact with a tappet (valve lifter) 4 provided at the upper end of the intake / exhaust valve to open and close the intake / exhaust valve. It is designed to be driven.

A link mechanism for transmitting the rotational power of the drive shaft 1 to the camshaft 2 is linked to a drive plate 5 fixed to the outer periphery of the drive shaft 1 via a flange 5 a of the drive plate 5 and a pin 6. Annular disc 7;
The annular disk 7 and the flange 2a of the camshaft 2
And a pin 8 for cooperating with. Annular disk 7
Is loosely fitted to the outer periphery of the drive shaft 1 through the gap S, and
Flange portion 2a of camshaft 2 and drive plate 5
In the axial direction with the flange portion 5a.

The variable mechanism for changing the lift characteristic of the intake / exhaust valve has a control disk 9 for supporting the outer periphery of the annular disk 7 so as to be relatively rotatable. By swinging by
The eccentric positions of the control disk 9 and the annular disk 7 with respect to the drive shaft 1 change. As a result, the rotation phase of the camshaft 2 with respect to the drive shaft 1 changes, and the lift characteristics are variably controlled.

Although not shown, a predetermined thrust clearance is set between the drive shaft 1 and a cylinder head that rotatably supports the drive shaft 1. Also, a predetermined thrust clearance is set between the camshaft 2, the annular disk 7, and the drive plate 5 arranged coaxially.

[0008]

A tappet 4 slidably fitted in a guide hole of a cylinder head.
It is necessary to use a pressing force from the cam lobe 3 to appropriately rotate around its own axis so that the sliding surface with the cylinder head is not unevenly worn. In order to rotate the tappet 4 in this manner, it is necessary to apply a pressing force of the cam lobe 3 to an axial position off the center of the tappet 4 to apply a rotational force to the tappet 4.

However, in the variable valve operating device as shown in FIG. 9, as described above, the thrust clearance is set between the drive shaft 1 and the cylinder head, and the camshaft 2 and the annular disk are provided. 7 and the drive plate 5 also have respective thrust clearances, so that the cam lobe 3 with respect to the tappet 4
Is relatively large in the thrust direction.

For this reason, even if the cam lobe 3 is offset with respect to the tappet 4, the pressing force from the cam lobe 3 acts on the center of the tappet 4 due to the above-mentioned positional variation and the like, and the tappet 4 4 cannot be satisfactorily rotated, and the above-mentioned uneven wear may occur.

The present invention has been made in view of such a problem, and in a variable valve operating device for an internal combustion engine, a tapping force of a cam lobe is reliably applied to an axial position deviated from the center of a tappet to thereby provide a tappet. The purpose of this is to make sure that is rotated.

[0012]

According to the present invention, there is provided a variable valve apparatus for an internal combustion engine according to the present invention, wherein a drive shaft that rotates in conjunction with the engine, a camshaft having a cam lobe for driving intake and exhaust valves on its outer periphery, A tappet interposed between the cam lobe and the intake / exhaust valve, a link mechanism that is wound around the drive shaft and one axial end of the cam shaft, and that transmits a driving force of the drive shaft to the cam shaft; And a variable mechanism that changes the lift characteristics of the intake and exhaust valves in cooperation with the link mechanism.

With such a configuration, when the driving force of the drive shaft is transmitted to the camshaft via the link mechanism, the cam lobe presses the tappet, and the intake and exhaust valves are opened and closed. Further, when the drive of the variable mechanism is controlled in accordance with the operating state of the engine, the lift characteristics of the intake and exhaust valves are variably controlled via the link mechanism.

Here, the camshaft has a shape in which the portion on the link connecting portion side in the axial direction is relatively close to the tappet because the link mechanism is connected to one end of the camshaft in the axial direction. . For this reason, the cam lobe makes strong contact with the tappet at the axial end on the link connecting portion side. Accordingly, the pressing position at which the cam lobe presses the tappet is shifted toward the link connecting portion with respect to the axial center of the cam lobe.

According to the first aspect of the present invention, the center of the cam lobe in contact with the tappet in the axial direction with respect to the center of the tappet is connected to a link connecting portion connecting the link mechanism and one end of the cam shaft in the axial direction. Is offset in the axial direction.

In other words, the cam lobe itself is offset with respect to the tappet in a direction in which the pressing position of the cam lobe itself is shifted with respect to the axial center.

As a result, the pressing position of the cam lobe is displaced in the axial direction toward the link connecting portion with respect to the center of the tappet by the sum of the shift amount of the pressing position of the cam lobe itself and the above-mentioned offset amount.

For this reason, even if the axial position of the cam lobe with respect to the tappet slightly varies due to the above-described thrust clearance or the like, the pressing position of the cam lobe is surely shifted from the center of the tappet toward the lift connection portion. And the tappet can be reliably rotated.

According to the second aspect of the present invention, the camshaft is fitted around the outer periphery of the drive shaft so as to be relatively rotatable, and the variable mechanism includes a control shaft extending substantially parallel to the drive shaft; A control cam provided on the outer periphery, wherein the link mechanism comprises: an eccentric cam provided on the outer periphery of the drive shaft; a ring-shaped link which is fitted to the outer periphery of the eccentric cam so as to be relatively rotatable; A rocker arm that is connected to the ring-shaped link at one end, and that is externally rotatably fitted to the outer periphery of the control cam, and a rod-shaped link that connects the rocker arm and one end of the camshaft in the axial direction. I have.

As described above, if the camshaft is fitted around the outer periphery of the drive shaft so as to be relatively rotatable, the components of the link mechanism can be integrated around the drive shaft to reduce the size. . In addition, since the connecting portion of the link mechanism comes into surface contact, the link mechanism has excellent wear resistance and is easy to lubricate.

According to the third and fourth aspects of the present invention, the cam lobes are provided at two locations on both sides in the axial direction with respect to one camshaft.
The cam lobe on the link connecting portion side relatively approaches the tappet due to a driving force or the like input from the drive shaft to the camshaft via the link mechanism.

As a result, the pressing force acting on the tappet from the cam lobe remote from the link connecting portion becomes relatively small, and there is a possibility that the rotational force acting on this tappet becomes insufficient. Further, there is a possibility that the cam lobe on the link connecting portion first presses the tappet, and the lift timing of the pair of intake and exhaust valves is shifted.

According to the third aspect of the present invention, the offset amount of the cam lobe far from the link connection portion is adjusted so that a sufficient rotational force acts on the tappet far from the link connection portion. It is characterized in that it is set relatively larger than the offset amount of the cam lobe on the side.

According to the fourth aspect of the present invention, the valve clearance between the cam lobe and the tappet far from the link connection portion is adjusted by the link connection so that both cam lobes simultaneously lift the tappet (intake / exhaust valve). The valve clearance is set to be relatively smaller than the valve clearance between the cam lobe and the tappet on the side closer to the section.

Further, as described above, a reaction force from the tappet to the anti-link connecting portion acts on the camshaft because the portion of the cam shaft on the lift connecting portion side relatively approaches the tappet. . For this reason, the thrust surface of the camshaft far from the link connecting portion is relatively easily worn.

According to a fifth aspect of the present invention, the thrust surface of the camshaft farther from the link connecting portion is brought closer to the link connecting portion in response to a reaction force acting on the cam shaft toward the opposite link connecting portion. It is characterized in that it is set relatively larger than the thrust surface of the camshaft on the side.

The invention according to claim 6 is characterized in that the tappet is of an inner shim type or a shimless type. That is, the cam lobe is configured to be in direct contact with the tappet so that the tappet rotates properly by the pressing force from the cam lobe.

According to a seventh aspect of the present invention, the outer periphery of the cam lobe is formed in a tapered shape in which a portion near the link connecting portion is relatively close to the tappet. In this case, the pressing position where the tappet is strongly pressed in the axial direction of the cam lobe is more reliably shifted to the link connecting portion side. That is, it is possible to give a greater difference in the surface pressure in the axial direction of the cam lobe.

[0029]

As described above, according to the present invention, since the pressing position of the cam lobe is surely shifted toward the link connecting portion with respect to the center of the tappet, the tappet can be surely rotated. The occurrence of uneven wear due to insufficient rotation of the tappet can be reliably suppressed.

[0030]

1 to 4 show an embodiment in which a variable valve apparatus according to the present invention is applied to an internal combustion engine provided with a pair of intake valves and exhaust valves for each cylinder. .

A drive shaft 12 that is continuous over all cylinders is provided above the cylinder head 10. The drive shaft 12 has a sprocket attached to one end (not shown) and rotates in conjunction with a crankshaft of the engine via a timing chain. The drive shaft 12 is formed in a hollow shape in which an axial oil passage 12a for introducing lubricating oil is formed. Also, an appropriate thrust clearance is set between the drive shaft 12 and the cylinder head 10 supporting the drive shaft 12 so that the drive shaft 12 rotates smoothly.

A hollow camshaft 14 divided for each cylinder is fitted around the outer periphery of the drive shaft 12 so as to be relatively rotatable. A pair of cam lobes 16 as swinging cams are integrally provided at two locations on both sides in the axial direction on the outer periphery of each cam shaft 14, and a journal 17 provided at an intermediate portion in the axial direction of these cam lobes 16 is provided with a lower bracket. 40
And the cylinder head 10 are rotatably supported.

Here, the cam lobe 16 on the side closer to the link connecting portion where one axial end (the left end in FIG. 1) of the cam shaft 14 and a rod-shaped link 30 of a link mechanism described later are connected to the cam lobe 16A and the link. The cam lobe 16 on the side farther from the connection portion is referred to as a cam lobe 16B. Similarly, in the intake valve 18 and the tappet 19 described later, the side near the link connection portion is referred to as the intake valve 18A and the tappet 19A, and the side farther from the link connection portion is suctioned. The valve 18B and the tappet 19B are used.

A cylindrical tappet 19 having a bottom is interposed between each cam lobe 16 and a pair of intake valves (or exhaust valves) 18 of each cylinder. Each tappet 19 is attached so as to cover the upper end of the stem of each intake valve 18, and is fitted into a guide hole 10 a of the cylinder head 10. On the other hand, as shown in FIG. 3, a retainer 46 for receiving one end of the valve spring 44 is fixed to the upper end of the stem of each intake valve 18. When each cam lobe 16 presses the tappet 19, the intake valve 18 is opened and closed against the reaction force of the valve spring 44.

Further, the tappet 19 is appropriately rotated around its own axis by the pressing force from the cam lobe 16.
There is no shim on the top, and the structure is in direct contact with the cam lobe 16. More specifically, the tappet 19 has a boss 1 as shown in FIG.
The stem end face of the intake valve 18 is in direct contact with the stem 9a, or a shim 48 of an appropriate thickness is provided between the boss 19a and the stem end face as shown in FIG. It is an interposed inner shim type.

The drive shaft 12 is located between the drive shaft 12 and one axial end of the camshaft 14 (the left end in FIG. 1).
A link mechanism for transmitting the rotational driving force of the intake valve 18 to the camshaft 14 is provided. A variable mechanism for changing the lift characteristic of the intake valve 18 is mechanically linked to the link mechanism.

This variable mechanism has a control shaft 24 extending substantially parallel to the drive shaft 12 and a control cam 26 provided on the outer periphery of the control shaft 24. The rotation of the control shaft 24 is controlled within a predetermined angle range by an actuator or the like (not shown) according to the operating state of the engine.
2 rotatably supported between an upper bracket 38 and a lower bracket 40 fastened and fixed to the cylinder head 10 side. The control cam 26 is integrally fixed to the outer periphery of the control shaft 24 by press fitting or the like, and is eccentric with respect to the axis of the control shaft 24 by a predetermined amount.

The link mechanism includes an eccentric cam 20 provided on the outer periphery of the drive shaft 12, a ring-shaped link 22 which is fitted to the outer periphery of the eccentric cam 20 so as to be relatively rotatable, and one end of the ring-shaped link 22. And a rocker arm 28 which is fitted to the outer periphery of the control cam 26 so as to be relatively rotatable.
And a rod-shaped link 30 connecting the rocker arm 28 and one end of the camshaft 14 in the axial direction.

The eccentric cam 20 is fixed to the outer periphery of the drive shaft 12 by press fitting or the like, and is eccentric with respect to the axis of the drive shaft 12 by a predetermined amount. In this embodiment, the eccentric cam 20 is formed integrally with a drive plate 21 fixed to the outer periphery of the drive shaft 12.
1, the camshaft 14 is configured to receive the axial end face, that is, the thrust faces 14a and 14b.
Note that the camshaft 14 and the eccentric cam 20 or the drive plate 2 are rotated so that the camshaft 14 rotates smoothly.
An appropriate thrust clearance is set between the two.

One end of the rocker arm 28 and the tip of the ring-shaped link 22 are connected to each other via a first pin 32 that penetrates both ends. Also, as shown in FIG. 1, one end of the camshaft 14 in the axial direction (left side in FIG. 1).
Is formed with a flange portion 15 facing the cam lobe 16A on the link connecting portion side. And the flange portion 15
By inserting the second pin 34 with one end of the rod-shaped link 30 interposed between the camshaft 14 and the cam lobe 16A, the camshaft 14 and the rod-shaped link 30 are connected to be rotatable relative to each other. I have. Further, the other end of the rod-shaped link 30 and the other end of the rocker arm 28 are relatively rotatably connected via a third pin 36 inserted therethrough.

With the above configuration, when the drive shaft 12 rotates around the shaft in synchronization with the rotation of the engine, the ring-shaped link 22 translates via the eccentric cam 20, and the rocker arm 28 correspondingly moves the control cam 26. , And the camshaft 14 swings about the axis of the drive shaft 12 via the rod-shaped link 30. As a result, the cam lobe swings and presses the tappet 19 to drive the intake valve 18 to open and close.

The control shaft 24 according to the operating state of the engine
Is rotationally controlled, the axial position of the control cam 26 serving as a swing fulcrum of the rocker arm 28 changes, and the lift characteristics of the intake valve 18, that is, the valve lift (operating angle) and the opening / closing timing are variably controlled. .

As described above, the camshaft 14 is connected to the drive shaft 1.
Since it is configured to be fitted around the outer circumference of the drive mechanism 2 so as to be relatively rotatable, the components of the link mechanism can be concentrated around the drive shaft 12 to reduce the size. Further, since the connecting portions of the link mechanism and the variable mechanism are in surface contact, they have excellent wear resistance and are easy to lubricate.

In the present embodiment, as shown in FIG. 1, the center of the tappet 19A is
The center in the axial direction of the cam lobe 16A that is in contact with the shaft is offset by a predetermined offset amount Xa toward the link connecting portion, that is, the left side in FIG. Similarly, with respect to the center of the tappet 19B, the cam lobe 16B contacting the tappet 19B
The center in the axial direction of the link connecting portion (the left side in FIG. 1)
Is offset by a predetermined offset amount Xb.

Next, the operation of the present embodiment will be described.

In the structure in which the tappet 19 slides in the guide hole 10a of the cylinder head 10 as in this embodiment,
In order to prevent uneven wear of the tappet 19, the cam lobe 16
It is necessary to rotate the tappet 19 around the axis by using the pressing force from

In particular, in the variable valve apparatus of the type in which the cam lobe 16 swings as in the present embodiment, the maximum lift shown in FIG. 5B from the start of the lift of the intake valve 18 shown in FIG. Until the time, the pressing force acting on the tappet 19 from the cam lobe 16 is always in a constant direction, so that the load is concentrated on the portions indicated by reference numerals 50 and 52 in FIG. As a result, uneven wear easily occurs on the outer peripheral surface of the tappet 19, and it is necessary to rotate the tappet 19 reliably.

In order to rotate the tappet 19, it is necessary that the pressing force of the cam lobe 16 acts on a position off the center of the tappet 19. According to the present embodiment, as shown in FIG. 1, the pressing positions Fa and Fb at which the pressing force is applied from the cam lobe 16 to the tappet 19 are reliably shifted in the axial direction from the center of the tappet 19 toward the link connecting portion. Can be.

More specifically, the camshaft 14 has a bearing portion at one location of the journal 17 at the center and is connected to the rod-shaped link 30 of the link mechanism at one end in the axial direction. Due to the rotational driving force transmitted from the drive shaft 12 via the link mechanism, the spring reaction force from the tappet 19, and the like, the shaft is inclined with respect to the axis of the drive shaft 12.

More specifically, in the initial state of the lift (the state shown in FIGS. 6 and 7) in which the cam lobe 16 begins to push the tappet 19 in the valve opening direction (downward in the figure), the link mainly from the drive shaft 12. Due to the rotational power transmitted to the camshaft 14 via the mechanism, the camshaft 14 is inclined such that the portion on the link connecting portion side approaches the tappet 19 side (the lower side in the figure). 6 and 7, the inclination of the camshaft 14 is exaggerated for the sake of clarity, and the actual inclination is extremely small.

For this reason, the cam lobes 16A and 16B are both connected to the tappet 19 at one axial end on the link connecting portion side.
A and 19B are strongly contacted, and the contact surface pressure at this portion becomes highest. That is, the cam lobes 16A and 16B are the tappet 1
Substantial pressing positions Fa and F that strongly press on 9A and 19B
“b” is displaced from the axial center of the cam lobes 16A, 16B toward the link connecting portion by the lengths La, Lb (see FIG. 1) of about half of the overall length in the axial direction.

In this embodiment, as shown in FIG. 1, the center of the cam lobes 16A and 16B is offset axially toward the link connecting portion with respect to the axial center of the tappets 19A and 19B (Xa, Xb). ). In other words,
The cam lobes 16A, 16B themselves are displaced in the tappet 19 in the direction in which the pressed positions Fa, Fb of the cam lobes 16A, 16B themselves are shifted.
A and 19B are offset.

As a result, as shown in FIG.
The deviation amounts La and Lb of the 6A and 16B themselves and the cam lobe 16
The sum of the offset amounts Xa, Xb of A, 16B (La + Xa, Lb + Xb), the cam lobes 16A, 16B
Of the tappets 19A and 19B are shifted axially toward the link connecting portion with respect to the centers of the tappets 19A and 19B.

Therefore, even if the axial positions of the cam lobes 16A, 16B with respect to the tappets 19A, 19B are slightly varied due to the above-described thrust clearance and the like, the pressing positions Fa,
Fb can be reliably eccentric from the center of the tappets 19A, 19B toward the lift connecting portion.

Therefore, when the cam lobes 16A, 16B press the tappets 19A, 19B, the cam lobes 16A, 16
A rotational moment acts on the tappets 19A and 19B along the traveling direction of the tappets 6B (see FIG. 4).
The shaft 19B can be surely rotated. As a result,
The occurrence of uneven wear due to insufficient rotation of the tappets 19A and 19B can be reliably suppressed.

In the initial stage of the valve lift shown in FIGS. 6 and 7, the cam lobe 16A on the link connecting portion side and the tappet 19A relatively approach due to the inclination of the cam shaft 14. As a result, the pressing force of the cam lobe 16 </ b> B farther from the link connecting portion becomes relatively small, and there is a possibility that the rotational moment acting on the tappet 19 becomes insufficient. Also, as shown in FIG. 7, first, the cam lobe 16A on the link connecting portion side.
Presses the tappet 19A, and the two intake valves 18A,
The lift timing of 18B may be shifted.

Therefore, the tappet 19 on the side opposite to the link connecting portion is used.
In order to apply a sufficient rotational force to B, preferably, the offset amount Xb on the side opposite to the link connecting portion is set to be larger than the offset amount Xa on the side of the link connecting portion (Xa <Xb).

In the example shown in FIG. 6, the cam lobes 1A and 16B lift the tappets 19A and 19B at the same time, so that the cam lobes 1A on the side farther from the link connecting portion are lifted.
The valve clearance between the tappet 19B and the tappet 19B is set to be relatively smaller by ΔC than the valve clearance between the cam lobe 16A and the tappet 19A on the link connection side.

The adjustment of the valve clearance amount is performed by selectively using shims 48 having different thicknesses in the case of the inner shim type shown in FIG. 3B, for example.

By the way, due to the inclination of the camshaft 14 and the like, a thrust reaction force acts on the camshaft 14 from the tappet 19 toward the anti-link connecting portion side (the right side in FIG. 1). Therefore, the thrust surface 14b of the camshaft 14 far from the link connecting portion is particularly easily worn.

Therefore, in this embodiment, as shown in FIG. 1, the thrust surface 14b farther from the link connection portion is set to be relatively larger than the thrust surface 14a of the camshaft 14 closer to the link connection portion. (Da <D
b).

FIG. 8 shows another embodiment of the present invention. Here, the outer periphery of each of the cam lobes 16A, 16B is axially close to the link connecting portion in the form of tappets 19A, 19B.
It is formed in a tapered shape so as to approach B. In this case, pressing positions Fa and Fb where the tappets 19A and 19B are strongly pressed in the axial direction of the cam lobes 16A and 16B.
Is more reliably shifted to the link connecting portion side. That is, the difference between the surface pressures of the cam lobes 16A and 16B in the axial direction can be increased.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a variable valve operating device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a sectional view of the variable valve apparatus of FIG. 1;

3A is a cross-sectional view showing a shimless type, and FIG. 3B is a cross-sectional view showing a tappet on an inner shim side.

FIG. 4 is a plan view of the variable valve apparatus of FIG. 1 as viewed from below.

FIGS. 5A and 5B are cross-sectional views of a main part at a lift start time and at a maximum lift time, respectively.

FIG. 6 is an explanatory diagram for explaining the operation of the present embodiment.

FIG. 7 is an explanatory diagram for explaining the operation of the present embodiment.

FIG. 8 is a configuration diagram showing another embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating a variable valve device for an internal combustion engine according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Drive shaft 14 ... Camshaft 16A, 16B ... Cam lobe 18A, 18B ... Intake valve 19A, 19B ... Tappet 20 ... Eccentric cam (link mechanism) 22 ... Ring link (link mechanism) 24 ... Control shaft (variable mechanism) 26 ... Control cam (variable mechanism) 28 ... Rocker arm (link mechanism) 30 ... Rod link (link mechanism)

Continuing from the front page (72) Inventor Shin Nakamura 1370 Onna, Atsugi-shi, Kanagawa F-term in Unisia Gex Co., Ltd. FA27 FA29 GA02

Claims (7)

[Claims] A drive shaft that rotates in conjunction with an engine; a camshaft having a cam lobe on an outer periphery for driving a suction / exhaust valve; a tappet interposed between the cam lobe and the suction / exhaust valve; A link mechanism that is wound around the drive shaft and one end in the axial direction of the camshaft to transmit the driving force of the drive shaft to the camshaft; and that the lift mechanism of the intake / exhaust valve is changed in cooperation with the link mechanism. A variable mechanism, with respect to the center of the tappet, the axial center of the cam lobe in contact with the tappet is axially moved to the link connecting portion side where the link mechanism and one axial end of the cam shaft are connected. A variable valve train for an internal combustion engine, characterized by being offset. 2. The camshaft is rotatably fitted to the outer periphery of the drive shaft so as to be relatively rotatable. The variable mechanism is provided on a control shaft extending substantially parallel to the drive shaft, and on the outer periphery of the control shaft. A control cam, wherein the link mechanism comprises: an eccentric cam provided on an outer periphery of the drive shaft; a ring-shaped link which is fitted to the outer periphery of the eccentric cam so as to be relatively rotatable; And a rod-shaped link connecting the rocker arm and one end in the axial direction of the camshaft. 2. The variable valve train for an internal combustion engine according to claim 1. 3. The cam lobes are provided at two locations on both sides in the axial direction with respect to one camshaft, and the offset amount of the cam lobe farther from the link connection portion is set to the offset amount of the cam lobe closer to the link connection portion. 3. The variable valve train for an internal combustion engine according to claim 1, wherein the variable valve train is set to be relatively larger than the variable valve train. 4. The cam lobe is provided at two positions on both sides in the axial direction with respect to one camshaft, and the amount of valve clearance between the cam lobe and the tappet farther from the link connection portion is set closer to the link connection portion. 3. The variable valve train for an internal combustion engine according to claim 1, wherein the valve clearance between the cam lobe and the tappet is set to be relatively smaller than the valve clearance. 5. The camshaft on the side farther from the link connection portion is set to be relatively larger than the thrust surface of the camshaft on the side closer to the link connection portion. 5. The variable valve operating device for an internal combustion engine according to any one of 4. 6. The variable valve train for an internal combustion engine according to claim 1, wherein the tappet is an inner shim type or a shimless type. 7. The internal combustion engine according to claim 1, wherein an outer periphery of the cam lobe is formed in a tapered shape such that a portion near the link connecting portion is relatively close to the tappet. Variable valve gear.