JP2000130130A - Variable valve system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable valve system of an internal combustion engine, capable of suitably alleviating impact load in switching of a cam while restraining performance of the internal combustion engine from being deteriorated. SOLUTION: A rocker arm 21 of a variable valve system is so arranged as to be relatively slid, and a movable cam follower 23 to be brought into contact with a high-speed cam 11, a roller cam follower 24 to be brought into contact with a low-speed cam 12, and a lock mechanism 30 for selectively regulating or allowing the sliding movement of the movable cam follower 23 are arranged on the rocker arm. Valve characteristics are variable by selectively switching a cam for opening and closing an engine valve to the low-speed cam 12 by allowing the sliding movement of the movable cam follower 23 or to the high-speed cam 11 by regulating the sliding movement. The lift change rate in the valve opening side ramp section in the cam profile of the high-speed cam 11 is set lower than that in the valve closing side ramp section of the high-speed cam 11 and in the valve opening and closing side ramp sections of the low-speed cam 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable valve operating apparatus for varying valve characteristics such as a valve lift and a working angle of an internal combustion engine. The present invention relates to a cam switching type variable valve apparatus in which valve characteristics are made variable by selectively switching cams to be opened and closed.

[0002]

2. Description of the Related Art In a four-cycle internal combustion engine, generally,
There is provided a valve operating device that opens and closes the engine valve by a cam that rotates synchronously with the engine output shaft.

In order to prevent the engine valve from being pushed up due to thermal expansion, a gap such as "valve clearance" or "tappet clearance" is usually provided in such a valve operating device, and the cam lift amount is equal to or more than the amount corresponding to this gap. Until, the engine valve is not actually driven to open and close. That is, of the cam lift amount, the range from the base circle of the cam, which is a range in which the engine valve is not substantially opened, to the cam lift amount corresponding to the gap is the “ineffective lift range”, A range equal to or greater than the invalid lift range in which the valve is opened is an “effective lift range”.

Further, as shown in FIG. 7, the cam is provided with sections at both ends of the cam lift curve where the amount of change in the cam lift, that is, the amount of change in the head change rate is very small. This section is generally called a “ramp section”. Such a ramp section may generate abnormal noise due to a collision of a cam against the cam follower of the rocker arm when the engine valve is opened, a collision of the rocker arm with the shaft end of the engine valve, or a collision of the engine valve with the valve seat when the valve is closed. It is set to suppress the deterioration of durability performance due to impact.

[0005] Conventionally, in order to improve the performance of an internal combustion engine, a variable valve actuating device for varying valve characteristics such as a lift amount and an operating angle of an engine valve has been developed and put into practical use. As one type of such a variable valve operating device, there is a variable valve operating device of a cam switching type in which the valve characteristics are variable by selectively switching a plurality of types of cams having different cam characteristics as described above. An apparatus described in Japanese Patent No. 42104 is known.

FIG. 8 shows a front sectional structure of the variable valve operating device described in the above publication. This variable valve apparatus is provided with a high-speed cam 110 corresponding to a high-speed operation state for each cylinder of the internal combustion engine.
And two low-speed cams 120 corresponding to the low-speed operation state. Also, the high-speed rocker arm 50 rotatable based on the pressing of the high-speed cam 110 and the two low-speed rocker arms 5 rotatable based on the pressing of the low-speed cam 120.
1 and 52 are supported by the rocker shaft 200.
The engine valve 13 is in contact with each of the low-speed rocker arms 51 and 52. And each low-speed rocker arm 51,
By pressing the engine valve 13 with the rotation of 52, the engine valve 13 is driven to open and close.

Further, the variable valve operating device allows the relative rotation between the high-speed rocker arm 50 and each of the low-speed rocker arms 51 and 52 to be fastened and released to allow the relative rotation. And a lock mechanism for selectively switching between a state where the rocker arms are individually rotated.

[0008] The lock mechanism is provided with each of the rocker arms 5 described above.
0 to 52 and cylinder holes 55 to 57 communicating with each other when their rotation phases coincide with each other, and a lock pin 53 slidably disposed in the cylinder holes 55 to 57.
And

The lock pin 53 is constantly urged toward the low-speed rocker arm 51 (the left side in FIG. 8) by the urging force of the coil spring 58. Further, a hydraulic chamber 54 defined by a lock pin 53 is formed in a cylinder hole 55 of the low-speed rocker arm 51. This hydraulic chamber 5
Reference numeral 4 communicates with an oil passage formed inside the rocker shaft 200 or the like, through which hydraulic oil is supplied to the hydraulic chamber 54 or discharged from the hydraulic chamber 54 through the oil passage. The hydraulic pressure in the hydraulic chamber 54 is adjusted by the supply and discharge of the hydraulic oil, and the lock pin 53 is set in each cylinder in accordance with the balance between the hydraulic pressure in the hydraulic chamber 54 and the biasing force of the coil spring 58. Hole 55-5
7 and its position is changed.

The lock pin 53 is inserted into each of the rocker arms 50 to 52 in each of the cylinder holes 55 to 57.
Between a predetermined position (restricted position) for restricting (locking) their relative rotation by engaging with the predetermined position (permissible position) for permitting their relative rotation by releasing the fastening. Reciprocating sliding based on control. FIG. 8 shows an aspect in which the lock pin 53 is located at the restriction position.

When the lock pin 53 is located at the regulating position, the rocker arms 50 to 52 are connected to each other, and the relative rotation of the rocker arms 50 to 52 is regulated (locked). In this way, the rocker arms 50 to 52 are integrally rotated based on the pressing of the high-speed cam 110 in which the cam lift amount and the cam working angle are set to be larger. Therefore, the engine valve 13 at this time is driven to open and close by the high-speed cam 11.

On the other hand, the relative rotation of the rocker arms 50 to 52 is allowed by the lock pin 53 being located at the above-described allowable position, and each of the rocker arms 50 to 52 is independently rotated by the pressing of the high-speed cam 110 and the low-speed cam 120. The engine valve 13 is driven to open and close by the low-speed cam 120. At this time, the high-speed rocker arm 5
Although 0 is rotated based on the pressing of the high-speed cam 110, its operation has no effect on the operation of the engine valve 13.

By the way, in this variable valve operating device, the cam profile of the high-speed cam 110 and the low-speed cam 120 is set as follows so as to suppress a decrease in engine output.

FIG. 9 is an enlarged view of a cam lift curve in each ramp section of these cams. In FIG. 9, a curve L1 represents a cam lift curve in a ramp section on the valve opening side of the high-speed cam 110, and a curve L2 represents a valve lift side on the valve closing side of the high-speed cam 110 and the valve opening side and valve closing side of the low-speed cam 120. The cam lift curve of each ramp section is shown.

As shown in FIG. 9, the slope of the cam lift curve L1 in the ramp section on the valve opening side of the high-speed cam 110 has a large inclination angle with respect to the cam lift curve L2 in the other ramp sections. The rate of change is set relatively large. This is for the following reason.

As described above, normally, in a valve train, in order to prevent the engine valve 13 from being pushed up due to thermal expansion or the like,
The above-mentioned "ineffective lift range" is set so that the cam lift does not substantially affect the opening / closing operation of the engine valve until the lift becomes equal to or higher than a predetermined height. This invalid lift range
Variations may occur due to dimensional tolerances, aging, and thermal deformation of the members. In particular, in the case of a variable valve train having the above-described lock mechanism, the variation in the invalid lift range tends to increase due to rattling on the fitting of the lock pin 53. Due to the variation of the invalid lift range,
The opening / closing timing of the engine valve 13 also fluctuates.

On the other hand, the magnitude of the fluctuation of the opening / closing valve timing decreases as the head change rate in the ramp section increases. As shown in FIG. 9, in the valve opening side ramp section of the high speed cam having a large lift change rate, the magnitude of the variation of the opening / closing valve timing with respect to the variation Δ of the invalid lift range is δ1, and the variation Δ in the other ramp sections. Is smaller than the magnitude δ2 of the change of the opening / closing valve timing with respect to.

Here, generally, a large variation in the opening / closing timing of the engine valve is not preferable in terms of the performance of the internal combustion engine. In particular, if a large fluctuation occurs in the valve opening timing of the intake valve, the period of the valve overlap also fluctuates excessively, so that the performance of the internal combustion engine is greatly affected.

Therefore, in the above-described variable valve operating apparatus, the variation in the size of the invalid lift range tends to be large, and the opening of the high-speed cam 110 has a large effect on the engine performance due to the variation in the valve opening timing. Variations in the valve opening timing are reduced by setting the head change rate in the valve side ramp section to be relatively large.

[0020]

By setting the rate of change of the head in the ramp section on the valve opening side of the high-speed cam 110 higher than that in the other ramp sections, fluctuations in the valve opening timing are reduced, and The performance of the engine is certainly maintained. However, such a setting may cause the following inconvenience when switching cams.

As described above, in the variable valve operating apparatus, when switching from the low-speed cam 120 to the high-speed cam 110, the lock pin 53 is moved to the regulating position to relatively rotate the rocker arms 50 to 52. Regulate (lock)
Let me. During such a cam switching operation, the lock pin 53 has not completely moved to the regulation position,
There is a period in which the relative rotation of each rocker arm 50 to 52 is not completely regulated (locked). If the high-speed rocker arm 50 is pushed down by the lift portion of the high-speed cam 110 during this period, the connection (fastening) between the high-speed rocker arm 50 and the low-speed rocker arms 51 and 52 is not complete, so the lock pin 53 is not provided. And each cylinder hole 55-5
7 may be damaged and durability and reliability of the variable valve operating device may be impaired.

Therefore, as in the variable valve operating device described above,
If the rate of change of the head in the ramp section on the valve-opening side of the high-speed cam 110 is set to be large, the depressing speed of the high-speed rocker arm 50 also increases, and the impact on the lock pin 53 further increases. That is, the above concerns about durability and reliability are promoted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an internal combustion engine that can appropriately reduce an impact load at the time of cam switching while suppressing performance degradation of the internal combustion engine. To provide a variable valve operating device.

[0024]

In order to achieve the above object, according to the present invention, a first cam and a second cam having different cam profile shapes and a rocker arm for opening and closing an engine valve are provided. A first follower provided and receiving the pressure of the first cam, a second follower also provided on the rocker arm and receiving the pressure of the second cam, the first follower and the second follower, And a lock mechanism for selectively engaging or releasing the lock. The engine valve is connected to the first cam in response to the release of the lock mechanism, and to the second cam in response to the engagement of the lock mechanism. In the variable valve operating apparatus for an internal combustion engine for selectively switching a cam to be opened and closed, a change rate of a head in a ramp section on a valve-opening side in a cam profile shape of the second cam is determined by the same. To the that were set smaller than the lift rate of change of the valve-closing side of the ramp section and the first cam opening side and the closing side of the ramp section of the cam and its gist.

According to the above configuration, the head change rate in the valve-opening ramp section in the cam profile shape of the second cam is set to be smaller than the head change rate in the other ramp sections. , The speed of the relative operation between the first and second followers in the valve-opening-side ramp section can be suppressed.

In the above-described variable valve operating system in which the cam for driving the opening and closing of the engine valve is switched by fastening or releasing the first and second followers, a large locking mechanism is used for switching the cam. An impact load may be applied. This impact load occurs when the lift of the second cam is started and the relative movement between the followers occurs before the fastening of the followers is completed. The impact load at this time can be reduced by reducing the rate of change of the head in the ramp section and reducing the operating speed of the relative motion between the followers.

However, if the head change rate in the ramp section is set small, the performance of the internal combustion engine may be reduced. This is because the smaller the head change rate, the larger the ratio of the fluctuation of the valve opening / closing timing of the engine valve to the deviation of the range of the cam lift amount (ineffective lift range) in which the engine valve is not actually opened. It is.

In this regard, according to the above configuration, only the lift change rate in the valve opening side ramp section of the second cam is set smaller than that in the other ramp sections. Variations in the opening / closing valve timing of the engine valve due to a change in the range can also be reduced. Therefore, it is possible to ensure the durability and reliability of the variable valve operating device while minimizing the performance deterioration of the internal combustion engine.

[0029] The invention described in claim 2 is the same as that in claim 1.
The variable valve operating device for an internal combustion engine according to claim 1, wherein the variable valve operating device is provided on both the intake side and the exhaust side of the engine, and is provided on both the intake side and the exhaust side of the engine. Of the second cam, the lift change rate of the ramp section on the valve opening side in the cam profile shape of the second cam is determined by the ramp section on the valve closing side of the second cam and the first cam section.
The gist is that the cam is set to be smaller than the head change rate in the ramp sections on the valve opening side and the valve closing side of the cam.

According to the above configuration, it is possible to ensure both durability and reliability of the variable valve gears on the intake side and the exhaust side of the engine. According to a third aspect of the present invention, in the variable valve operating system for an internal combustion engine according to the first aspect, the variable valve operating system is provided on both the intake side and the exhaust side of the engine. Only for the cam provided on the exhaust side of the engine, the lift change rate of the valve-opening ramp section in the cam profile shape of the second cam is determined by the valve-closing ramp section of the second cam and The gist is that the first cam is set to be smaller than the head change rate in the ramp section on the valve opening side and the valve closing side of the first cam.

Variations in the valve overlap period between the exhaust valve closing timing and the intake valve opening timing greatly affect the performance of the internal combustion engine. Therefore, it is preferable to suppress fluctuations in the closing timing of the exhaust valve and the opening timing of the intake valve as much as possible. In this regard, according to the above configuration, only the head change rate in the valve opening side ramp section of the high-speed cam provided on the exhaust side is set to be small. Thus, the durability and reliability of the variable valve device provided on the exhaust side can be ensured.

The invention described in claim 4 is the first invention.
In the variable valve operating device for an internal combustion engine according to any one of the above (1) to (3), at least one of a cam lift height and a cam working angle of the second cam is set to be larger than that of the first cam. Is the gist.

According to the above configuration, only the head change rate in the ramp section on the valve closing side of the second cam is set to be large, and the fluctuation of the valve closing timing is suppressed. When the cam lift height or the cam working angle is set to be large, the influence of the fluctuation of the opening / closing valve timing of the engine valve on the performance of the engine tends to increase. Therefore, by suppressing the fluctuation of the valve closing timing at the time of driving the opening and closing of the engine valve by the second cam,
It is possible to suppress a decrease in performance of the engine.

The invention described in claim 5 is the same as the invention described in claim 4.
Wherein the second follower is a movable cam follower slidably disposed on the rocker arm, and the lock mechanism includes a lock pin slidably disposed. And the movement of the movable cam follower with respect to the rocker arm is regulated at a first sliding position of the lock pin, and is released at a second sliding position different from the first sliding position. In a variable valve apparatus of a type in which the sliding of a movable cam follower disposed on a rocker arm is switched or closed by a lock pin to switch a cam that opens and closes an engine valve, the movable cam follower is opened and closed by a second cam. The pressing of the second cam is transmitted to the rocker arm by the contact between the lock pin and the lock pin. Therefore, the impact of the above-mentioned impact which may occur when switching from the first cam to the second cam becomes particularly large. In this regard, according to the above configuration, the impact load can be reduced, and the reduction in durability and reliability can be significantly suppressed.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying a variable valve operating device for an internal combustion engine according to the present invention will be described below.

First, in the variable valve operating apparatus according to the present embodiment, a structure for selectively switching a cam to vary valve characteristics of an engine valve and its function will be described with reference to FIGS.
This will be described in detail with reference to FIG.

FIG. 1 shows the front structure near the rocker arm of the variable valve operating apparatus according to the present embodiment, and FIG. 2 shows the side structure similarly near the rocker arm. As shown in FIGS. 1 and 2, in this variable valve operating device, the camshaft 10 has two types of cams 11,
12 are provided. Among these cams, the cam 11 is a high-speed cam in which at least one of the cam lift amount and the cam working angle is set larger.
Is a low-speed cam in which at least one of the cam lift and the cam working angle is set smaller.

On the other hand, below the camshaft 10 provided with the cams 11 and 12, a rocker arm 21 rotatably supported by a rocker shaft 20 is provided. An arm 22 is provided on the tip side of the rocker arm 21. The tip of the arm 22 is in contact with the upper ends of the pair of engine valves 13 (FIG. 2), and is pressed by the urging force of the valve spring 14 (FIG. 2) of the engine valves 13 to the side where the valves 13 are closed. ing. Then, as described above, the arm valve 22 that swings with the rotation of the rocker arm 21 presses the engine valve 13 so that the engine valve 13 is driven to open and close.

On the upper surface of the rocker arm 21, a movable cam follower 23 capable of contacting the high-speed cam 11 and a roller cam follower 24 capable of contacting the low-speed cam 12 are provided. The roller cam follower 24 is rotatably supported by the rocker arm 21. The roller cam follower 24 is in rolling contact with the low-speed cam 12, receives the pressure, and can transmit the pressure of the cam 12 to the rocker arm 21.

On the other hand, the movable cam follower 23 is disposed slidably in the vertical direction with respect to the rocker arm 21. The movable cam follower 23 is constantly pressed toward the high-speed cam 11 by the urging force of the coil spring 25.
Therefore, the movable cam follower 23 comes into sliding contact with the high-speed cam 11 and receives the pressing force.

Further, the rocker arm 21 is provided with a lock mechanism 30 for selectively allowing or restricting (locking) relative sliding of the movable cam follower 23 to the rocker arm 21 based on hydraulic control. This lock mechanism 3
Hydraulic oil used for the operation of the rocker shaft 2
The oil is supplied or discharged through a rocker shaft oil passage 43 formed in the locker arm 0 and a rocker arm oil passage (not shown in FIGS. 1 and 2) formed in the rocker arm 21. As the operating oil for operating the lock mechanism 30, a part of the lubricating oil used for lubricating various parts of the internal combustion engine is used. The detailed configuration and operation of the lock mechanism 30 will be described later.

When the movable cam follower 23 is allowed to slide relative to the rocker arm 21 by the lock mechanism 30, the movable cam follower 23 has no relation to the rotation of the rocker arm 21 (the swing of the arm 22).
It is slid in the vertical direction based on the pressing of the high-speed cam 11 independently.

The urging force of the coil spring 25 for urging the movable cam follower 23 toward the high-speed cam 11 is set sufficiently smaller than the urging force of the valve spring 14 of the engine valve 13. Therefore, when the relative sliding of the movable cam follower 23 with respect to the rocker arm 21 is permitted, the pressing force of the high-speed cam 11 is almost absorbed by the movable cam follower 23,
It is not transmitted to the rocker arm 21 as a force large enough to drive the engine valve 13. Therefore, the rocker arm 21 at this time rotates (oscillates) based on the pressing of the low speed cam 12 transmitted through the roller cam follower 24, and the engine valve 13 opens and closes according to the cam profile shape of the cam 12. It will be driven.

On the other hand, when the relative sliding is restricted (locked) by the lock mechanism 30, the pressing of the high speed cam 11 is performed via the movable cam follower 23 and the rocker arm 21.
Will be transmitted to Therefore, the rocker arm 21 at this time is rotated (oscillated) based on the pressing of the high-speed cam 11 having a larger cam lift amount and cam working angle, and the engine valve 13 has the cam profile shape of the cam 11. Is driven to open and close in accordance with.

In the variable valve operating apparatus of the present embodiment, basically, the cam for driving the opening and closing of the engine valve 13 is selectively switched in this manner, so that the valve characteristics are variable. Next, the detailed configuration and operation of the lock mechanism 30 will be described.

FIGS. 3 and 4 are cross-sectional views showing a side cross-sectional structure of the lock mechanism 30. FIG. FIG. 3 shows a state in which the relative sliding is allowed, and FIG. 4 shows a state in which the relative sliding is restricted (locked).

As shown in FIGS. 3 and 4, the movable cam follower 23 abutting on the high-speed cam 11 (FIGS. 1 and 2) has a sliding hole 35 penetrating the rocker arm 21 in the vertical direction.
It is slidably loosely fitted inside. Rocker arm 2
1 has a cylinder hole 3 intersecting with the sliding hole 35.
6 are formed in the front-rear direction. The lock pin 31 is slidably loosely fitted in the cylinder hole 36. The lock pin 31 is always urged by the urging force of the coil spring 33 in the direction away from the slide hole 35, that is, in the base end direction of the rocker arm 21.

The tip of the lock pin 31 has a groove 32
Are formed. The lower end of the movable cam follower 23 can be fitted into the groove 32. The bottom surface of the rocker arm 21 in the groove 32 is notched, and when the lock pin 31 is located on the base end side of the rocker arm 21 as shown in FIG. Is allowed to slide up and down. That is, the fastening of the movable cam follower 23 to the rocker arm 21 (the roller cam follower 24) is released.

On the other hand, a bottom surface is left at the base end side of the rocker arm 21 in the groove 32, and when the lock pin 31 is located at the tip end side of the rocker arm 21, as shown in FIG. Abuts against the bottom surface of the groove 32 to restrict (lock) sliding of the follower 23 in the above-described manner. That is, the movable cam follower 23 is fastened to the rocker arm 21 (roller cam follower 24).

In the cylinder hole 36 in which the lock pin 31 is provided, a base space 34 defined by the lock pin 31 has a hydraulic pressure for introducing hydraulic oil for sliding the lock pin 31. Room. This hydraulic chamber 3
4 is connected to a rocker arm oil passage 49 formed in the rocker arm 21. This rocker arm oil passage 4
9 communicates with the rocker shaft oil passage 43 (FIGS. 1 and 2). The supply and discharge of hydraulic oil to and from the hydraulic chamber 34 are performed through the oil passages 43 and 49, so that the hydraulic pressure in the hydraulic chamber 34 is adjusted.

That is, when the movable cam follower 23 is allowed to slide relative to the rocker arm 21, the hydraulic chamber 3
The hydraulic oil is discharged from the inside of the chamber 4 and the oil pressure in the same chamber 34 is reduced. As the oil pressure drops, the lock pin 31
The rocker arm 21 is moved to a predetermined position (allowable position) on the base end side by the urging force of No. 3. As a result, as shown in FIG. 3, the lower end of the movable cam follower 23 is located at a portion where the bottom surface on the distal end side of the groove 32 is notched, and the relative sliding in the vertical direction is allowed. At this time, since the pressing of the high-speed cam 11 is hardly transmitted to the rocker arm 21 as described above, the rocker arm 21 is swung by the low-speed cam 12 (FIGS. 1 and 2).

On the other hand, when restricting (locking) the relative sliding of the movable cam follower 23, hydraulic oil is supplied into the hydraulic chamber 34 to increase the hydraulic pressure in the same chamber 34. The lock pin 31 moves to a predetermined position (restriction position) on the distal end side of the rocker arm 21 while resisting the urging force of the coil spring 33 as the hydraulic pressure rises. When the lock pin 31 moves in this manner, the bottom surface of the movable cam follower 23 is located at a portion where the bottom surface on the base end side of the groove 32 is left as shown in FIG. Come into contact. As a result, the pressing of the high-speed cam 11 is directly transmitted to the rocker arm 21 through the contact between the movable cam follower 23 and the lock pin 31. In this case, as described above, the rocker arm 21 is swung by the high-speed cam 11 in which at least one of the cam lift amount and the cam working angle is set larger.

Next, the behavior of the lock pin 31 and the movable cam follower 23 during such cam switching will be described with reference to FIG. FIG. 5 shows an enlarged cross-sectional structure of the distal end portion of the lock pin 31 and the lower end portion of the movable cam follower 23 of the variable valve operating device of the present embodiment. FIG.
FIG. 5A shows a state when the lock pin 31 is located at the above-described allowable position, and FIG. 5B shows a state when the lock pin 31 is located at the above-mentioned restriction position.

As shown in FIG. 5A, the lock pin 3
When the movable cam follower 2 is located at the allowable position,
The lower end of the lock pin 31 is located in a portion 32 a of the lock pin 31 where the bottom surface of the groove 32 is cut out, and the relative sliding of the movable cam follower 23 with respect to the rocker arm 21 is allowed. When the lock pin 31 is located at the regulation position as shown in FIG. 5B, the lower end of the movable cam follower 23 is located at the portion 32b where the bottom surface of the groove 32 of the lock pin 31 is left. At this time, the entire lower end of the movable cam follower 23 contacts the portion 32b where the bottom surface of the groove 32 is left.
The pressure of the high-speed cam 11 can be sufficiently received.

However, in the lock mechanism 30 having the above-described structure, there is a period during which the lock pin 31 is not completely moved to the regulation position during the switching operation from the low-speed cam 12 to the high-speed cam 11. When the movable cam follower 23 is pushed down by the lift portion of the high-speed cam 11 during such a cam switching operation, as shown in FIG. It comes into contact with the movable cam follower 23.

At this time, the lower end of the movable cam follower 23 has a portion 3 where only the bottom surface of the groove 32 is left.
Since they are not in contact with 2b, very high surface pressure is applied to these contact surfaces against the pressing of the high-speed cam 11.
The surface pressure may cause damage to the movable cam follower 23 and the lock pin 31. Further, in some cases, the impact at the time of contact with the movable cam follower 23 causes
The lock pin 31 may be pushed back to the allowable position side. Thus, the reliability and durability of the variable valve operating device are impaired.

The lock pin 3 is moved during the movement.
Even if the first cam 1 comes into contact with the movable cam follower 23 or is pushed back due to the impact at the time of the contact, the lowering of the high-speed cam 11 by the lift portion is temporarily completed until the next pressing down is started. Since the pin 31 can move to a predetermined restriction position, the cam can be switched.

In order to reduce such damage at the time of cam switching, in the variable valve operating device of the present embodiment, the following improvements are made to the cam profile shape. FIG.
(A) shows the high-speed cam 11 of the variable valve operating device of the present embodiment.
3 shows a cam lift curve of the low-speed cam 12. FIG. 6B is an enlarged view of a ramp section of the cam lift curves of the cams 11 and 12.

In the variable valve apparatus of this embodiment, the head change rate in the ramp section of the high speed cam 11 and the low speed cam 12 is, as shown in FIG. 6B, the valve opening side Ho of the high speed cam 11. Of the high-speed cam 11 on the valve closing side H
c, and the valve-opening side Lo and the valve-closing side Lc of the low-speed cam 12.
Is set small with respect to the head change rate. Therefore, the operating speed of the engine valve 13 (the speed at which the movable cam follower 23 is pushed down) in the valve opening side ramp section of the high-speed cam 11 is relatively low.

In the variable valve operating apparatus of the present embodiment, the maximum lift amount (ramp height) h in the ramp section is the same on both the valve-opening side and the valve-closing side of each of the cams 11 and 12. I have. Therefore, the length of the ramp section, that is, the rotation phase angle of the camshaft corresponding to the ramp section, is determined by the ramp section length b on the valve closing side of the high-speed cam 11 and the ramp opening side and valve closing side of the low-speed cam 12. The ramp section length a on the valve opening side of the high-speed cam 11 is set to be longer than the section length c (a> b, c).

The above-described collision between the movable cam follower 23 and the lock pin 31 occurs immediately after the high-speed cam 11 starts to push down the movable cam follower 23, that is, in the valve-opening side lamp section Ho of the cam 11. Occurs when a push is taking place. Therefore, by setting only the head change rate in the valve opening side ramp section Ho of the high-speed cam 11 to a relatively small value, the impact applied to the lock mechanism 30 is reduced, and its durability and reliability are maintained. Will be able to do it.

As described above, if the head change rate in the ramp section is set small, the opening / closing timing of the engine valve 13 fluctuates according to the change in the invalid lift range, which is not preferable in terms of the performance of the internal combustion engine. However, in the variable valve operating device of the present embodiment, as described above, only the head change rate in the valve opening side ramp section (Ho) of the high-speed cam 11 is set to be relatively small, and in other sections, that is, for the high-speed cam. The lift change rates of the ramp sections on the valve closing side (Hc) of the cam 11 and the valve opening side (Lo) and the valve closing side (Lc) of the low-speed cam 12 are set to be sufficiently large. As a result, these sections (Hc, L
o, Lc), the change in the on-off valve timing of the engine valve 13 due to the change in the invalid lift range becomes relatively small,
The adverse effects on the performance of the internal combustion engine are also minimal.
That is, in the variable valve operating device of the present embodiment, only the head change rate in the ramp section on the valve opening side of the high-speed cam 11 is set to be smaller than in the other ramp sections, so that the performance degradation of the internal combustion engine is minimized. While ensuring the durability and reliability of the lock mechanism 30.

As described above, according to the variable valve apparatus for an internal combustion engine of the present embodiment, the following effects can be obtained. (1) The head change rate in the valve opening side ramp section Ho of the high-speed cam 11 is determined by the valve closing side ramp section Hc of the high-speed cam 11 and the valve opening side and valve closing side ramp section Lo, of the low-speed cam 12.
By setting it to be smaller than Lc, the impact applied to the lock mechanism 30 can be reduced, and its durability and reliability can be maintained high.

(2) Since only the head change rate in the valve opening side ramp section Ho of the high-speed cam 11 is set relatively small, the head change rates in the other ramp sections Hc, Lo, Lc are relatively small. Is set to be large. As a result, it is possible to minimize the increase in the fluctuation of the opening / closing valve timing of the engine valve 13 due to the reduction of the head change rate in the valve opening side ramp section Ho of the high-speed cam 11, and to reduce the performance of the internal combustion engine. Can also be minimized.

Note that the embodiment of the present invention may be modified as follows. In the variable valve apparatus of the above embodiment, each of the cams 11 and 12
By setting the ramp height h on the valve-opening side and the valve-closing side to be the same and changing the ramp section lengths a, b, and c, the head change rate in the valve-opening ramp section Ho of the high-speed cam 11 can be relatively reduced. However, the above setting can also be made by appropriately adjusting the lamp height of these ramp sections, or by adjusting the ramp section length and the lamp height, respectively.

Also, in the variable valve operating device of the above embodiment, the head change rates in the ramp sections on the valve closing side of the high speed cam 11 and the valve opening side and valve closing side of the low speed cam 12 are all set to be the same. However, if it is set to be larger than the head change rate in the ramp section on the valve opening side of the high-speed cam 11, even if there is a difference between the head change rates in these sections, the effects of the present embodiment will be obtained. The same effect can be obtained.

In the case of an internal combustion engine having a variable valve device of a cam switching type for both the intake system and the exhaust system, the variable valve device according to the present invention, that is, the engine valve is pressed in accordance with the engagement of the lock mechanism. Variable valve train with the lift change rate in the ramp section on the valve-opening side of the cam that is smaller than that in the other ramp sections is applied to only one of the systems, or to both systems It is good also as a structure which performs. When the variable valve apparatus according to the present invention is applied to both the intake system and the exhaust system, both the durability and reliability of the variable valve apparatuses provided in both of these systems can be secured.

In particular, when the variable valve device according to the present invention is applied only to the exhaust system, the performance of the internal combustion engine can be greatly suppressed from deteriorating. This is for the following reason. Variations in the valve overlap period between the closing timing of the exhaust valve and the opening timing of the intake valve greatly affect the performance of the internal combustion engine. Therefore, it is preferable to suppress fluctuations in the closing timing of the exhaust valve and the opening timing of the intake valve as much as possible. Therefore, by setting only the head change rate in the valve opening side ramp section of the high-speed cam provided on the exhaust side to be small, the fluctuation of the bubble overlap period is suppressed, and the deterioration of the performance of the internal combustion engine is significantly suppressed. In addition, the durability and reliability of the variable valve device provided on the exhaust side can be secured.

In the variable valve apparatus of the above embodiment, the high speed cam 11 is in sliding contact with the movable cam follower 23, and the low speed cam 12 is in rolling contact with the roller cam follower 24. These cams 11,
Twelve contact modes are not limited to this. For example, the high-speed cam 11 and the low-speed cam 12 are configured to be in rolling contact, or the high-speed cam 11 is in rolling contact with the low-speed cam 12.
The side may make a sliding contact. That is, the present invention can be applied regardless of the contact state of the cam.

The ramp section in which the head change rate is set relatively small is not limited to the valve opening side ramp section of the high-speed cam 11 as in the variable valve apparatus of the above embodiment. The ramp section in which the head change rate is set relatively small as described above becomes active when the relative movement between members independently operated by a plurality of types of cams having different cam profile shapes is activated, and the engine valve Is a valve opening side ramp section of a cam that drives the opening and closing of the cam, and the cam to be set may have a different configuration depending on the configuration of the variable valve operating device.
For example, the high-speed cam directly presses the rocker arm, and the low-speed cam presses the movable cam follower disposed so as to be able to move relative to the rocker arm,
A lock mechanism that regulates the relative movement of the movable cam follower such that the low-speed cam and the movable cam follower abut on the contact portion between the high-speed cam and the rocker arm at a position closer to the rotational axis of the cam shaft. In a variable valve operating device such as a variable valve operating device that switches the cam by restricting or allowing the relative movement of a member operated based on the pressing of the low speed cam, the low speed cam valve opening side ramp section By setting the rate of change of the head in this example smaller than in the other ramp sections, it is possible to obtain an effect similar to the effect of the present embodiment.

The present invention includes a plurality of rocker arms which are individually rotated by pressing a plurality of types of cams, as shown in FIG. 8, and connects or separates these rocker arms from each other. Thus, the present invention can be similarly applied to a variable valve apparatus having a mechanism for switching a cam that drives an engine valve to open and close. In essence, it is provided with members each operated by a plurality of types of cams having different cam profile shapes, and a cam for opening and closing the engine valve based on the operation of a lock mechanism that selectively restricts or permits relative movement between these members. If the variable valve actuation device changes the valve characteristics by selectively switching over, it is possible to obtain an effect similar to that of the above embodiment by setting a cam profile shape according to the above embodiment. .

[0072]

According to the first aspect of the present invention, the head change rate of the valve-opening ramp section in the cam profile shape of the second cam is set smaller than the head change rate of the other ramp sections. As a result, it is possible to ensure the durability and reliability of the variable valve operating device while minimizing performance degradation of the internal combustion engine.

Further, according to the second aspect of the invention, it is possible to ensure both the durability and the reliability of the variable valve apparatus on the intake side and the exhaust side of the engine. Also,
According to the third aspect of the present invention, since only the head change rate in the valve opening side ramp section of the high-speed cam provided on the exhaust side is set to be small, while suppressing the fluctuation of the bubble overlap period, In addition, durability and reliability of the variable valve device provided on the exhaust side can be ensured.

According to the fourth aspect of the present invention, only the head change rate in the valve closing side ramp section of the second cam is set to be large, and the fluctuation of the valve closing timing is suppressed. Can be minimized.

According to the fifth aspect of the present invention, the impact load can be reduced, and the reduction in durability and reliability can be greatly suppressed.

[Brief description of the drawings]

FIG. 1 is a front view showing the vicinity of a rocker arm of an embodiment of a variable valve operating device for an internal combustion engine according to the present invention.

FIG. 2 is a side view showing the vicinity of a rocker arm of the variable valve operating device.

FIG. 3 is a sectional view showing a structure of a lock mechanism of the variable valve operating device.

FIG. 4 is a sectional view showing a structure of a lock mechanism of the variable valve operating device.

FIG. 5 is an enlarged sectional perspective view of the vicinity of a lock pin tip of a lock mechanism of the variable valve operating device.

FIG. 6 is a graph showing a cam lift curve of a cam of the variable valve operating device.

FIG. 7 is a graph showing a cam lift curve of a conventional valve train.

FIG. 8 is a sectional view showing a front sectional structure of a conventional variable valve operating device.

FIG. 9 is a graph showing a cam lift curve of a conventional variable valve device.

[Explanation of symbols]

10 camshaft, 11, 110 high-speed cam, 12
... Cam for low speed, 13 ... Engine valve, 14 ... Valve spring, 20 ... Rocker shaft, 21 ... Rocker arm, 2
2 ... arm, 23 ... movable cam follower, 24 ... roller cam follower, 25 ... coil spring, 30 ... lock mechanism, 3
1 ... lock pin, 32 ... groove, 33 ... coil spring, 34 ...
Hydraulic chamber, 35: sliding hole, 36: cylinder hole, 43: rocker shaft oil passage, 49: rocker arm oil passage.

Claims (5)

[Claims] A first cam and a second cam having different cam profile shapes, a first follower provided on a rocker arm for driving an engine valve to open and close, and receiving a pressure from the first cam; And a lock mechanism for selectively fastening or unfastening the first follower and the second follower. A variable valve apparatus for an internal combustion engine that selectively switches a cam for opening and closing the engine valve to the first cam in response to the release and to the second cam in accordance with the engagement of the lock mechanism; The change rate of the head in the valve opening side ramp section in the cam profile shape of the second cam is determined by the valve closing side ramp section of the second cam and the valve opening side and valve closing of the first cam. A variable valve operating device for an internal combustion engine, wherein the variable valve operating device is set to be smaller than a head change rate in a side ramp section. 2. The variable valve apparatus is provided on both the intake side and the exhaust side of the engine. The cam provided on both the intake side and the exhaust side of the engine includes The lift change rate in the valve-opening ramp section of the cam profile shape of the second cam is determined by comparing the valve-opening ramp section of the second cam and the valve-opening and valve-closing side ramp sections of the first cam. 2. The variable valve train for an internal combustion engine according to claim 1, wherein the variable valve train is set smaller than a head change rate. 3. The variable valve apparatus is provided on both the intake side and the exhaust side of the engine, and only the cam provided on the exhaust side of the engine is provided with the second cam. The head change rate in the valve-opening ramp section in the cam profile shape is calculated as the head change rate in the valve-opening-side ramp section of the second cam and the valve-opening and valve-closing-side ramp sections of the first cam. 2. The variable valve operating device for an internal combustion engine according to claim 1, wherein the variable valve operating device is set smaller than the variable valve operating device. 4. The internal combustion engine according to claim 1, wherein at least one of a cam lift height and a cam working angle of the second cam is set to be larger than that of the first cam. Variable valve gear. 5. The second follower is a movable cam follower slidably disposed on the rocker arm. The lock mechanism has a lock pin slidably disposed, and the lock mechanism has a lock pin with respect to the rocker arm. 5. The internal combustion engine according to claim 4, wherein the movement of the movable cam follower is regulated at a first sliding position of the lock pin, and the movement is released at a second sliding position different from the first sliding position. Variable valve gear of the engine.