JPH084514A - Valve train for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a valve operating system for an internal combustion engine capable of accurately and reliably transmitting the opening and closing timings of two cams to the intake and exhaust valves at low cost. A first rocker arm 12, which is rockably supported by a rocker shaft 13, is linked to an intake / exhaust valve 11, and is driven by a first cam 15, and rocks on a first rocker arm 12 or a rocker shaft 13. Freely supported by the second cam 23
Driven by the second rocker arm 21, a lost motion mechanism for the second rocker arm 21, a first position supported by the first rocker arm 12, and a second position at which the lost motion mechanism exerts its function and its function is stopped. A swingable linking member 36, linking switching means for switching the linking member 36 between the first position and the second position, and the first rocker arm and the second rocker arm in a state where the lost motion mechanism stops its function. And position adjusting means capable of adjusting the relative position with respect to.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve operating system for an internal combustion engine capable of switching the opening / closing timing of intake / exhaust valves according to the operating condition of a vehicle.

[0002]

2. Description of the Related Art An internal combustion engine mounted on an automobile is required to flexibly cope with a very large rotation change and load change. From such a viewpoint, a valve operating system for an internal combustion engine in which the opening / closing timing of the intake / exhaust valve can be changed according to the operating state of the vehicle has been proposed, for example, in Japanese Patent Laid-Open No. 5-171909, and a load on the internal combustion engine Regardless of the engine speed or engine speed, it is designed to always obtain stable and efficient output characteristics.

In the valve operating system for an internal combustion engine disclosed in Japanese Patent Laid-Open No. 5-171909, a first rocker arm that abuts an intake valve or an exhaust valve is swingably attached to a rocker shaft and driven by a first cam. The second rocker arm driven by the second cam is freely attached to the first rocker arm, and the lost motion mechanism is incorporated between the second rocker arm and the first rocker arm. A linking member swingable between a first position where the mechanism exerts its function and a second position where the lost motion mechanism stops its function is attached to the first rocker arm, and the first position and the second position of this linking member are further attached. A linkage switching means for switching to the position is provided.

That is, when the linkage member attached to the first rocker arm is moved to the first position where the lost motion mechanism exerts its function by the linkage switching means, the connection between the first rocker arm and the second rocker arm is released, The opening / closing timing by the first cam is given to the intake valve or the exhaust valve. Further, when the linking member is moved to the second position where the lost motion mechanism stops its function, the first rocker arm and the second rocker arm are connected, and the opening / closing timing by the second cam is applied to the intake valve or the exhaust valve. To be

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the conventional valve operating device for an internal combustion engine disclosed in Japanese Patent No.
When the linkage member attached to the first rocker arm is moved to the second position where the lost motion mechanism stops its function by the linkage switching means, the relative position between the first rocker arm and the second rocker arm must be set appropriately. It becomes difficult to engage the linking member with the step portion of the second rocker arm. As a result, the first rocker arm and the second rocker arm cannot be integrally connected, and there is a possibility that the opening / closing timing by the second cam cannot be selected. On the contrary, even if the linking member is moved to the second position and the linking member can be engaged with the step portion of the second rocker arm, play occurs in the second rocker arm with respect to the first rocker arm and the second rocker arm is connected. A striking sound is generated between the member and the member, and the opening / closing timing of the second cam may not be accurately transmitted to the intake valve and the exhaust valve.

For this reason, the above-mentioned Japanese Patent Laid-Open No. 5-17190.
In the conventional valve operating device for an internal combustion engine disclosed in Japanese Patent No.
There is a problem that the dimensional accuracy of the parts is required to be maintained at a considerably high level, and the assembling accuracy of these parts must be high, resulting in an extremely high manufacturing cost.

[0007]

An object of the present invention is to provide an internal combustion engine capable of accurately and reliably transmitting the opening / closing timings of two cams to an intake valve and an exhaust valve at low cost without increasing the dimensional accuracy and assembly accuracy of parts. It is to provide the valve operating device of.

[0008]

A valve operating system for an internal combustion engine according to the present invention includes a first rocker arm which is swingably supported by a rocker shaft, is linked to an intake valve or an exhaust valve, and is driven by a first cam. A first rocker arm, or a second rocker arm swingably supported by the rocker shaft and driven by a second cam, a lost motion mechanism for the second rocker arm, and a first rocker arm. And a linking member swingable between a first position where the lost motion mechanism exhibits its function and a second position where the lost motion mechanism stops its function, and the first position and the second position of the linking member. To the first rocker arm and the second rocker arm in a state in which the function of the lost motion mechanism is stopped. It is characterized in that comprises the position adjusting means capable of adjusting the relative positions of the arm.

Here, it is possible to form a recess in the second rocker arm and house the lost motion mechanism in this recess. In this case, it is effective to configure the lost motion mechanism by a compression spring housed in the recess and a lost motion plunger whose tip comes into contact with the first rocker arm by the spring force of the compression spring.

Similarly, it is possible to form a recess in the first rocker arm and store the lost motion mechanism in this recess. In this case, it is effective to configure the lost motion mechanism by a compression spring housed in the recess and a lost motion plunger whose tip comes into contact with the second rocker arm by the spring force of the compression spring.

Further, the position adjusting means may be incorporated in the lost motion mechanism. In this case, the position adjusting means changes the protruding length of the lost motion plunger with respect to the concave portion in a state where the function of the lost motion mechanism is stopped. It is possible.

On the other hand, the position adjusting means may be provided on the first rocker arm or the second rocker arm so as to face the lost motion mechanism. In this case, the tip end of the position adjusting means contacts the lost motion plunger. The protrusion length along the facing direction with the lost motion plunger can be changed by contact.

[0013]

According to the present invention, when the linking member attached to the first rocker arm is moved to the first position where the lost motion mechanism exhibits its function by the linking switching means, the first rocker arm and the second rocker arm are connected. It is released and the opening / closing timing by the first cam is given to the intake valve or the exhaust valve.

When the linking member is moved to the second position where the lost motion mechanism stops its function, the first rocker arm and the second rocker arm are connected to each other, and the opening / closing timing by the second cam is the intake valve or the exhaust valve. Given to the valve.

The relative position of the first rocker arm and the second rocker arm in the state where the lost motion mechanism has stopped its function can surely move the link member to the second position, and the link member moves to the second position. The position adjusting means appropriately adjusts the play of the second rocker arm with respect to the first rocker arm in the moved state.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the valve operating system for an internal combustion engine according to the present invention is applied to an internal combustion engine in which two intake valves are incorporated in one cylinder (hereinafter, simply referred to as an engine) will be described with reference to the drawings. Detailed description will be made with reference to FIGS.

That is, each cylinder of the engine is provided with a first rocker arm 12 corresponding to two intake valves 11, and the base end of this first rocker arm 12 is attached to each cylinder head (not shown). It is swingably supported on a hollow main rocker shaft 13 common to the cylinders.
The first rocker arm 1 formed into a substantially U-shaped bifurcation
Two low speed cams 15 as first cams of the present invention, which are formed on the left and right sides of 2 on both sides of the main rocker shaft 13 in parallel with the cam shaft 14 arranged in parallel with the main rocker shaft 13, respectively, come into contact with each other. Two cam slippers 16 are joined to each other, and the tops of the valve rods 17 of the two intake valves 11 are in contact with the tips of the first rocker arms 12 by the spring force of the valve springs 18, respectively. ing.

On the sub-rocker shaft 20 having both ends snap-locked to the shaft bracket 19 formed on the upper end of the first rocker arm 12, the base end of the second rocker arm 21 rocks with respect to the first rocker arm 12. It is movably supported. The slipper surface 22 formed at the tip of the second rocker arm 21 is in contact with the high-speed cam 23 as the second cam of the present invention formed on the cam shaft 14.

On the lower side of the second rocker arm 21, there is formed a stepped blind hole 24 having a circular cross section which is opened downward as a recess of the present invention. The large diameter portion of the stepped blind hole 24 is Lost motion plunger with cup-shaped cross section 2
5 is slidably fitted. A washer 29 that abuts a step portion 28 of the stepped stop hole 24 is attached to a screw shaft 27 with which the ball head 26 is locked to the lost motion plunger 25, and is located in a small diameter portion of the stepped stop hole 24. The adjustment nut 30 and the fixing nut 31 for preventing the loosening thereof are screwed. Further, a compression spring 32 for pressing the lost motion plunger 25 against the ball head 26 is interposed between the washer 29 and the lost motion plunger 25.

The lost motion mechanism in this embodiment has the above-mentioned lost motion plunger 25 and compression spring 32, and the position adjusting means is a screw shaft 27 and a washer 29.
The adjustment nut 30 and the fixing nut 31 are included in the stepped blind hole 24 in the form of a unit. And the screw shaft 27
By adjusting the amount of screwing of the adjusting nut 30 with respect to the stopper nut, the ball head 26 of the screw shaft 27 integrated with the lost motion plunger 25 from the step portion 28 of the stepped blind hole 24 in a state where the function of the lost motion mechanism is stopped.
The amount of protrusion to the lower end of can be changed arbitrarily.

In order to facilitate relative rotation between the screw shaft 27 and the adjusting nut 30, in this embodiment, a notch groove 33 for locking a tool (not shown) at the upper end of the screw shaft 27.
Is engraved, and while holding the adjustment nut 30 with a wrench or the like, engage a tool such as a screwdriver in the notch groove 33,
By relatively rotating these, the screwing amount of the adjusting nut 30 with respect to the screw shaft 27 can be adjusted.

In the present embodiment, the lost motion plunger 25 and the screw shaft 27 are separately assembled, but they may be integrally joined. In any case, they move integrally. The spring force of the compression spring 32 pushes the ball head 26 against the plunger contact portion 34 formed in the central portion of the first rocker arm 12 in a spot facing state, and the reaction force causes the slipper surface 22 of the second rocker arm 21 to move at high speed. It always comes into contact with the working cam 23.

On the other hand, the lever bracket 35, which is formed in a bifurcated shape at the lower portion of the first rocker arm 12, has both ends of a lever holding shaft 37 which swingably supports a switching lever 36 functioning as a connecting member of the present invention. Is the main rocker axis 1
The second rocker arm 21 is mounted in parallel with the third rocker arm 21.
An engaging step portion 38 that can engage with the upper end portion of the switching lever 36 is formed at the lower end of the tip of the.

On the side of the upper end of the switching lever 36, the switching lever 36 is provided in parallel with the lever holding shaft 37.
Is formed with a release plunger receiver 39 projecting from the side. A releasing plunger 41 is slidably fitted in a blind hole 40 formed in the first rocker arm 12 so that the opening faces the releasing plunger receiver 39, and the stopper is closed by the releasing plunger 41. A compression spring 42 for pressing the releasing plunger 41 against the releasing plunger receiver 39 is housed in the hole 40. That is, by the spring force of the compression spring 42, the switching lever 36 is urged in the direction in which the engagement with the engagement step portion 38 of the second rocker arm 21 is released via the release plunger 41 and the release plunger receiver 39. Has been done.

Further, at the lower end of the switching lever 36,
An engagement plunger receiving portion 43 is formed, and an oil chamber 44 formed in the first rocker arm 12 so that an opening faces the engagement plunger receiving portion 43 has an engagement chamber for abutting the engagement plunger receiving portion 43. A plunger 45 is slidably mounted. The other end of the oil passage 46 formed in the first rocker arm 12 and one end of which is connected to the oil chamber 44 faces the outer peripheral surface of the main rocker shaft 13, and the oil passage 46 and the oil formed in the main rocker shaft 13 are formed. The passage 47 is the main rocker shaft 1
3 is in a communication state via a communication passage 48 formed in the radial direction.

Pressure oil from an oil pump (not shown) is introduced into the oil passage 47 of the main rocker shaft 13 via a switching valve (not shown). In this embodiment, based on the engine speed, cooling water temperature, lubricating oil temperature, supercharging pressure, throttle valve opening, etc., basically, when the engine speed is equal to or higher than a predetermined speed, When the rotational speed of the engine is less than a predetermined speed, the pressure oil in the oil passage 47 is discharged to the oil sump side (not shown), and the engine torque is smoothly changed so as not to suddenly change. It is supposed to be.

Here, when the pressure oil from the oil pump is supplied into the oil chamber 44, the engagement plunger 45 is pushed out toward the first rocker arm 12 side against the spring force of the compression spring 42, and the switching lever 36. The upper end of the second rocker arm 2
The second locker arm 21 is held in the second position where the lost motion mechanism stops its function by engaging the engagement step portion 38 of No. 1. On the contrary, when the pressure oil in the oil passage 47 is discharged to the oil sump side by the switching valve, the engagement plunger 45 is oiled by the spring force of the compression spring 42 via the engagement plunger receiving portion 43 of the switching lever 36. While being pushed back to the chamber 44 side, the upper end portion of the switching lever 36 and the engagement step portion 38 of the second rocker arm 21 are disengaged, and the second motion rocker arm 21 is brought to the first position where the lost motion mechanism exerts its function. Is retained.

The low speed cams 15 and the high speed cams 23 formed therebetween have different contours so as to satisfy the valve lift characteristics required at low engine speed and high engine speed. Formed into a shape, generally high-speed cam 2
3 has a cam profile in which at least one of the valve lift amount and the valve opening period is larger than that of the low speed cam 15.

Therefore, when the engine is in the low speed region, the first rocker arm 12 swings according to the cam profile of the low speed cam 15 to open / close each intake valve 11. At this time, although the second rocker arm 21 is swung by the high speed cam 23, the switching lever 36 is at the position shown in FIG. 4 due to the spring force of the compression spring 42, and the lost motion mechanism performs its function first. It is in a linked state at the position. Therefore, the second rocker arm 21 oscillates with respect to the first rocker arm 12 about the sub-rocker shaft 20, and accordingly, the lost motion plunger 25 moves together with the screw shaft 27, the adjusting nut 30, and the fixing nut 31 into the compression spring 3.
It only slides in the stepped blind hole 24 with the bending of 2, and the movement of the first rocker arm 12 is not hindered.

On the other hand, when the engine is in the high speed region, the pressure oil from the oil pump is supplied from the oil passage 47 to the oil chamber 44 via the communication passage 48 and the oil passage 46 via the switching valve. Therefore, the engagement plunger 45 pushes against the engagement plunger receiving portion 43 against the spring force of the compression spring 42,
The switching lever 36 rotates counterclockwise in FIG. 4 about the lever holding shaft 37, and the upper end portion thereof engages with the engagement step portion 38 of the second rocker arm 21.
Switches to the position shown by the solid line in FIG. 6 and enters the linked state at the second position where the lost motion mechanism stops its function. As a result, the first rocker arm 12 and the second rocker arm 21 are integrally connected, the low speed cam 15 is separated from the first rocker arm 12, and the second rocker arm 21 and the high speed cam 23 together with the first rocker arm 12. According to the cam profile of (3), the main rocker shaft 13 is swung.

In this case, the high-speed cam 23 is formed so that both the valve opening and the valve lift amount are larger than those of the low-speed cam 15, so that the second rocker arm 21 becomes the first rocker arm 12. In the integrated state, each intake valve 1
The valve opening amount and the valve lift amount of 1 are both large.

When the engine shifts from the high speed region to the low speed region again, the pressure in the oil chamber 44 decreases due to the operation of the switching valve, so that the spring force of the compression spring 42 reduces the pressure oil in the oil chamber 44. As a result of overcoming the pressure and moving the switching lever 36 and the actuating plunger 31 to the position shown in FIG. 4, the restraint of the second rocker arm 21 is released, and the lost motion mechanism again becomes in a state of exerting its function.

In this way, the torque characteristic based on the cam profile of the low speed cam 15 and the torque characteristic based on the cam profile of the high speed cam 23 are combined, and the engine is driven from the low rotation region to the high rotation region. The torque can be increased.

By the way, the switching lever 36 is engaged with the engagement step portion 38 in a state where the high-speed cam 23 is not brought into contact with the slipper surface 22 of the second rocker arm 21 as in the assembly of the valve gear. At this time, when the play of the second rocker arm 21 with respect to the first rocker arm 12 is large, that is, when the swing amount of the second rocker arm 21 around the sub rocker shaft 20 is large, the adjustment nut 30 described above is attached to the ball head 26.
Since the amount of protrusion of the lost motion plunger 25 from the stepped blind hole 24 is reduced by screwing in the side, the second rocker arm 2 with respect to the first rocker arm 12
The play of 1 can be reduced. As a result, it is possible to reduce the impact sound generated between the second rocker arm 21 and the switching lever 36, and at the same time prevent damage caused by this impact.

However, the adjusting nut 30 for the ball head 26 side
If the screwing amount of is too large, the upper end of the switching lever 36 collides with the front end face of the second rocker arm 21 when the switching lever 36 at the first position is moved to the second position, and the switching lever 36 is Since it becomes impossible to engage with the engagement step portion 38, it is necessary to adjust the screwing amount of the adjusting nut 30 to an appropriate amount so that the screwing amount of the adjusting nut 30 is not excessive.

In the above-mentioned embodiment, the position adjusting means composed of the screw shaft 27, the adjusting nut 30 and the like is incorporated into the lost motion mechanism to form one unit, but these are separately arranged so as to be opposed to each other. It is also possible to arrange them.

As shown in FIG. 8 showing the sectional structure of another embodiment of the present invention, the second rocker arm 21 has a circular cross-section which is downwardly opened as a concave portion of the present invention, on the lower side of the second rocker arm 21. A hole 49 is formed. A lost motion plunger 50 having a stepped cup-shaped cross section with a smaller diameter on the lower end side is slidably fitted into the blind hole 49, and the blind hole 49 closed by the lost motion plunger 50 is inserted into the blind hole 49. The compression spring 53 that presses the lost motion plunger 50 against the ball head 52 at the upper end of the adjusting screw 51 screwed to the central portion of the first rocker arm 12 is housed in the. A snap ring 54 that engages with a step formed on the outer circumference of the lost motion plunger 50 is attached to the inner peripheral wall near the opening of the blind hole 49.
The maximum protruding amount of the lost motion plunger 50 from 9 is regulated. Then, when the lost motion plunger 50 reaches the maximum protruding amount, the switching lever 36 is rotated from the first position to the second position, and the upper end thereof is locked by the engagement step portion 38.

The lost motion mechanism of the present invention has the lost motion plunger 50, the compression spring 53, and the snap ring, and urges the lost motion plunger 50 to the plunger contact portion 26 of the first rocker arm 12. The reaction force of 53 causes the slipper surface 22 of the second rocker arm 21 to move to the high-speed cam 23.
It always comes into contact with.

The adjusting screw 51 includes the first rocker arm 12
The fixing nut 55 for preventing the adjusting screw 51 from loosening is tightened together, and the adjusting screw 5 for the first rocker arm 12 is
By adjusting the screwing amount of No. 1, the protruding amount of the ball head 52 at the upper end of the adjusting screw 51 facing the lower end of the lost motion plunger 50 can be changed, and this state is held by the fixing nut 55. There is. The adjusting screw 51 and the fixing nut 55 correspond to the position adjusting means in the present invention.

Therefore, at the time of assembling the valve operating device, the lost motion plunger 50 is set to the maximum protruding amount, the lower end of the lost motion plunger 50 is brought into contact with the ball head 52 of the adjusting screw 51, and the engaging step 38 is switched to. When the lever 36 is engaged, the upper end of the switching lever 36 and the engagement step 38
The play of the second rocker arm 21 with respect to the first rocker arm 12 can be reduced when the high-speed cam 23 is assembled by screwing the adjustment screw 51 into the first rocker arm 12 so that the gap between the first rocker arm 12 and the first rocker arm 12 can be reduced. . As a result, it is possible to reduce the impact sound generated between the second rocker arm 21 and the switching lever 36, and at the same time prevent damage caused by this impact.

However, if the adjusting screw 51 is screwed into the first rocker arm 12 side too much, the upper end of the switching lever 36 is moved to the second position when the switching lever 36 in the first position is moved to the second position. Since the switching lever 36 cannot be engaged with the engagement step 38 because it collides with the front end surface of the rocker arm 21, the screwing amount of the adjusting screw 51 is adjusted to an appropriate amount so that the screwing amount is not excessive. What is necessary is the same as in the previous embodiment.

The other construction may be exactly the same as that of the previous embodiment, and the members having the same functions as those of the previous embodiment shown in FIGS. 1 to 7 in FIG. 8 are designated by the same reference numerals. There is. Also,
Although the lost motion mechanism is attached to the second rocker arm 21 side in the above-described embodiment, it is naturally possible to attach it to the first rocker arm 12 side. In this case, the position adjusting means can be incorporated in the lost motion mechanism or attached to the second rocker arm 21 so as to face the lost motion mechanism, as in the above-described two embodiments.

In each of the above-described embodiments, the second rocker arm 21 is connected to the first rocker arm 12 and the auxiliary rocker shaft 20.
Although the rocker is rotatably supported via the base rocker shaft 13, the base end portion of the second rocker arm 21 may be rockably supported on the main rocker shaft 13. In this case, the sub rocker shaft 20
Can be omitted.

[0044]

According to the valve operating system for an internal combustion engine of the present invention,
Since the position adjusting means that can adjust the relative position of the first rocker arm and the second rocker arm in the state where the lost motion mechanism has stopped its function is provided, the play of the second rocker arm with respect to the first rocker arm is minimized, and The impact sound between the two rocker arms and the connecting member can be suppressed, and the opening / closing timing by the second cam can be accurately transmitted to the intake valve and the exhaust valve.

Therefore, the dimensional accuracy and the assembly accuracy of the parts can be lowered as compared with the conventional one, and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment in which a valve train for an internal combustion engine according to the present invention is applied to a cylinder in which two intake valves are incorporated.

FIG. 2 is a side view of the embodiment shown in FIG.

FIG. 3 is a front view of the embodiment shown in FIG.

4 is a sectional view taken along the line IV-IV in FIG. 1 in a state where the lost motion mechanism exhibits its function.

5 is a sectional view taken along the line VV in FIG.

6 is a sectional view taken along the line IV-IV in FIG. 1 in a state where the lost motion mechanism has stopped its function.

FIG. 7 is a cutaway view in which the lost motion mechanism and the position adjusting means are extracted and enlarged in the present embodiment.

FIG. 8 is a sectional view of a portion of a second rocker arm according to another embodiment of the present invention.

[Explanation of symbols]

 11 intake valve 12 first rocker arm 13 main rocker shaft 14 cam shaft 15 low speed cam 16 cam slipper 17 valve rod 18 valve spring 19 shaft bracket 20 auxiliary rocker shaft 21 second rocker arm 22 slipper surface 23 high speed cam 24 stepped stop hole 25 Lost Motion Plunger 26 Ball Head 27 Screw Shaft 28 Step 29 Washer 30 Adjustment Nut 31 Fixed Nut 32 Compression Spring 33 Notch Groove 34 Plunger Abutment 35 Lever Bracket 36 Switching Lever 37 Lever Holding Shaft 38 Engaging Step 39 Plunger receiver for release 40 Blind hole 41 Plunger for release 42 Compression spring 43 Engagement plunger receiver 44 Oil chamber 45 Engaging plunger 46 Oil passage 47 Oil passage 48 Communication passage 49 Stop hole 50 Lost motion plunger 51 Adjustment screw 52 Ball head 53 Compression spring 54 Snap ring 55 Fixing nut

Claims (10)

[Claims] 1. A first rocker arm rockably supported by a rocker shaft, linked to an intake valve or an exhaust valve, and driven by a first cam; and a first rocker arm or a rocker shaft rocking the rocker shaft. A second rocker arm that is freely supported and driven by a second cam; a lost motion mechanism for the second rocker arm; a first position that is supported by the first rocker arm and that the lost motion mechanism exerts its function; A linking member swingable to a second position where the lost motion mechanism stops its function; a linking switching means for switching the linking member to the first position and the second position; and the lost motion mechanism. Position adjusting means capable of adjusting the relative position of the first rocker arm and the second rocker arm in a state where its function is stopped, A valve gear of an internal combustion engine, characterized in that comprises a. 2. The valve operating system for an internal combustion engine according to claim 1, wherein the lost motion mechanism is housed in a recess formed in the second rocker arm. 3. The lost motion mechanism has a compression spring housed in the recess, and a lost motion plunger whose tip abuts against the first rocker arm by the spring force of the compression spring. The valve operating device for an internal combustion engine as described above. 4. The valve operating system for an internal combustion engine according to claim 1, wherein the lost motion mechanism is housed in a recess formed in the first rocker arm. 5. The lost motion mechanism has a compression spring housed in the recess and a lost motion plunger whose tip abuts against the second rocker arm by the spring force of the compression spring. The valve operating device for an internal combustion engine as described above. 6. A valve operating system for an internal combustion engine according to claim 1, 2, 3 or 4 or 5, wherein the position adjusting means is incorporated in a lost motion mechanism. . 7. The position adjusting means is capable of changing the protruding length of the lost motion plunger with respect to the concave portion in a state in which the lost motion mechanism has stopped its function. A valve operating system for an internal combustion engine according to claim 6. 8. A valve operating system for an internal combustion engine according to claim 2, wherein the position adjusting means is provided on the first rocker arm so as to face the lost motion mechanism. 9. A valve operating system for an internal combustion engine according to claim 4, wherein the position adjusting means is provided on the second rocker arm so as to face the lost motion mechanism. 10. The position adjusting means is characterized in that the tip of the position adjusting means is in contact with the lost motion plunger so as to be able to change the protruding length along the facing direction of the lost motion plunger. Item 9. A valve train for an internal combustion engine according to Item 9.