JP2002242624A - Variable valve system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable valve system capable of facilitating the control of various items of characteristics over the whole rotation range by decreasing the number of three-dimensional cams and setting off the can width large, enhancing the easiness to mount on an internal combustion engine by suppressing the increment in the overall height, and securing the high-speed followup performance by suppressing the increase of the mass of the valve system. SOLUTION: A direct striking valve lifter 10 is equipped with two lifter bodies 11 having an end wall 12 and a cylindrical peripheral wall 13, a lifter bridge 20 installed in a bridged form as including a pressing part 22 and central part 21 and prevented from rotating as it is engaged with the lifter bodies 11, and a follow-up contacting mechanism installed on the lifter bridge 20 and contacting with the three-dimensional cams 2. Each lifter body 11 is furnished at the end wall 12 with a retainer structure part consisting of a cotter fitting part 17 and a spring seat part 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable valve mechanism for continuously or stepwise changing a valve timing and a lift amount from a low rotation to a high rotation of an internal combustion engine.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 7-45803 discloses a continuous variable valve mechanism using a three-dimensional cam whose cam profile changes in the axial direction. Since it is desired to make the length (hereinafter, referred to as a cam width) larger than a general cam, it is difficult to form a large number of three-dimensional cams densely on a camshaft.

In order to solve this problem, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 0-28092928 discloses that a plurality of cylindrical valve lifters are connected by a connecting member having a swing follower for the three-dimensional cam, thereby reducing the number of three-dimensional cams and increasing the cam width. A valve mechanism is disclosed.

[0004]

However, Japanese Patent Application Laid-Open No.
In the variable valve mechanism disclosed in Japanese Patent No. 280929, a connecting member (a bracket in the embodiment) having an oscillating follower is added above the valve lifter. Had a mounting problem. In addition, the mass of the valve train increases by the amount of the connecting member, and there is a possibility that the high-speed followability is reduced.

Accordingly, an object of the present invention is not only to facilitate the control of various characteristics over the entire rotation range by reducing the number of three-dimensional cams and increasing the cam width, but also to suppress the increase in the overall height to achieve an internal combustion engine. It is an object of the present invention to provide a variable valve mechanism capable of improving the mountability on a vehicle or suppressing the increase in the mass of the valve operating system and ensuring high-speed followability.

[0006]

In order to achieve the above object, a variable valve mechanism according to the present invention has a cam profile continuously changed in the axial direction from a cam profile for low rotation to a cam profile for high rotation. A three-dimensional cam, a displacement device for displacing the three-dimensional cam in the axial direction according to an operation state such as the rotation speed of the internal combustion engine, and a direct-hit type for opening and closing a valve by reciprocating based on a cam profile of the three-dimensional cam. In the variable valve mechanism having a valve lifter, the direct-acting valve lifter presses two or more (at least two) lifter bodies each having an end wall and a cylindrical peripheral wall, and presses the end wall of each lifter body. A lifter bridge that is provided in a bridge shape including a pressing portion and a central portion located substantially at the center with respect to each pressing portion, and is prevented from rotating by being engaged with each lifter body. A follow-up contact mechanism that is provided on the lifter bridge and includes a follow-up contact portion that contacts the three-dimensional cam while following a change in the contact line angle accompanying the rotation of the three-dimensional cam. A retainer structure is provided, which is fitted to a cotter engaged near a base end of the valve and receives one end of a valve spring.

Here, the retainer structure is not particularly limited, but is provided at a central portion inside each end wall to be fitted to the cotter and at a circumferential portion inside each end wall. And a spring seat that receives one end of the valve spring.

The end wall is preferably provided with a relief hole into which the base end of the valve enters. The escape hole includes not only a through hole but also a recess with a bottom. When the escape hole is a through hole, it is preferable that a stopper member for pressing the base end face of the valve to prevent the valve from being removed is attached to the escape hole.
Although this retaining member is not particularly limited, the following (a)
(B) can be illustrated. (A) A retaining member comprising a pressing spring that absorbs the dimensional variation of each part and presses the base end surface of the valve, and a stopper that locks the escape hole and stops the pressing spring. (B) A retaining member formed of a holding spring that locks in the escape hole and absorbs the dimensional variation of each part to press the base end surface of the valve.

In addition, the vicinity of the base end of the valve and the cotter are
It is also preferable that the valve is engaged with a clearance in a direction perpendicular to the axis of the valve so as to absorb a dimensional variation of each part.

The engagement between each lifter body and the lifter bridge is not particularly limited, but the following modes (1) and (2) can be exemplified. (1) Engagement by fitting a convex portion provided outside each end wall with a concave portion provided in each pressing portion. It is preferable that the convex portion and the concave portion are fitted so as to be relatively rotatable so as not to hinder the rotation of each lifter body around the central axis. The recess is
Includes through holes as well as bottomed recesses. (2) Engagement by fitting a part of the outer peripheral surface of each peripheral wall and a guide part extending from the central part toward the part so as to be relatively rotatable. The guide portion preferably has a concave circular arc surface substantially matching the outer peripheral surface of each peripheral wall.

The following contact mechanism is not particularly limited, but includes a semi-cylindrical inner seat provided at the center of the lifter bridge and a following contact part fitted to the semi-cylindrical inner seat so as to be able to roll. preferable. This follow-up contact portion may be a replacement part for adjusting the valve clearance. In addition, a roller mechanism with a follow-up contact portion disclosed in JP-A-9-296714 can be applied.

The valve timing phase, valve opening angle and lift amount in the low rotation cam profile, and the valve timing phase in the high rotation cam profile,
The valve opening duration and the lift amount can be appropriately set according to the requirements of each internal combustion engine. However,
In many cases, the cam profile for low rotation has a small valve opening angle and the lift amount, and the cam profile for high rotation has a large valve opening angle and the lift amount.

When the three-dimensional cam is displaced stepwise by the displacement device, the three-dimensional cam may be changed in two steps. In this case, it is preferable that the two-step displacement can be adjusted. More preferably, the three-dimensional cam is displaced in at least three steps. Most preferably, the three-dimensional cam is continuously displaced. The displacement device is not limited to a specific structure, but may be a device using hydraulic pressure, electromagnetic force, or the like.

Next to the low-rotation cam profile side of the three-dimensional cam, an idle rotation cam whose cam profile does not change in the axial direction is juxtaposed, and the follow-up contact portion comes into contact with the three-dimensional cam when the internal combustion engine is rotating under load. Load rotating contact surface
It is preferable that an idle rotation contact surface that comes into contact with the idle rotation cam during idle rotation of the internal combustion engine is provided side by side. Further, it is preferable that a gap is provided between the three-dimensional cam and the idle rotation cam to allow a boundary portion between the load rotation contact surface and the idle rotation contact surface of the following contact portion to escape.

The variable valve mechanism of the present invention can be applied to either an intake valve or an exhaust valve, but is preferably applied to both.

Also, the present technical idea is widely applicable to a valve operating mechanism, in which a retainer structure portion is fitted to an end wall of a lifter main body to be fitted to a cotter engaged with a portion near a base end of a valve and to receive one end of a valve spring. May be included.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a variable valve mechanism in which the present invention is applied to both an intake valve and an exhaust valve will be described below with reference to the drawings. Therefore, in the embodiment, simply referring to a valve refers to both an intake valve and an exhaust valve.

First, FIGS. 1 to 5 show a variable valve mechanism according to the first embodiment. The camshaft 1 has a cam from a low-speed cam profile on the right to a high-speed cam profile on the left in FIG. A three-dimensional cam 2 whose profile is continuously changed in the axial direction is formed. The three-dimensional cam 2 includes a base circular portion 2a and a nose portion 2b. The base circular portion 2a has the same radius in both the low-rotation cam profile and the high-rotation cam profile, and thus has a cylindrical surface without inclination. However, since the nose portion 2b has a small valve opening action angle and a lift amount in the low rotation cam profile and has a large valve opening action angle and the lift amount in the high rotation cam profile, the nose portion 2b is inclined like a conical surface. I have.

At the end of the camshaft 1, there is provided a displacement device (not shown) for continuously displacing the camshaft 1 and the three-dimensional cam 2 in the axial direction according to the operating conditions such as the rotational speed of the internal combustion engine. I have. The displacement device includes a guide portion of the camshaft 1 using splines and a camshaft 1 using hydraulic pressure.
, And is controlled by a control device such as a microcomputer that operates based on a rotation sensor of the internal combustion engine, an accelerator opening sensor, and the like.

Below the camshaft 1, a direct-acting valve lifter 10, which opens and closes two adjacent valves 4 at the same time by reciprocating in the illustrated example based on the cam profile of the three-dimensional cam 2, is provided. ing. The two valves 4 are intake valves (or exhaust valves) provided double in one cylinder.

The direct-acting valve lifter 10 includes two lifter bodies 11 each having a disk-shaped end wall 12 and a cylindrical peripheral wall (skirt part) 13, and a pressing portion for pressing the end wall 12 of each lifter body 11. A lifter bridge 20 that is provided in a bridge-like shape including a central portion 21 that is located substantially at the center with respect to each pressing portion 22 and that is prevented from rotating by engaging with each lifter main body 11; A follow-up contact mechanism that includes a follow-up contact portion 30 that is provided on the stereoscopic cam 2 and contacts the three-dimensional cam 2 while following a change in the contact line angle accompanying the rotation of the three-dimensional cam 2.

An end wall 12 of each lifter main body 11 is provided with a retainer structure for receiving one end of the valve spring 6 while being fitted to the cotter 3 engaged near the base end of the valve 4. The retainer structure is provided at a central portion inside the end wall 12 and is fitted with a tapered cylindrical cotter fitting portion 17 to be fitted to the cotter 3, and is provided at a circumferential portion inside the end wall 12 to provide a valve A spring seat 18 for receiving one end of the spring 6;

Further, a convex portion 14 to be described later is provided at a central portion outside the end wall 12, and the convex portion 14 is provided with a relief hole 35 into which the base end of the valve 4 enters. The escape hole 35 of this example is a through hole, and an engagement groove 36 is formed on the inner peripheral surface thereof. A retaining member for pressing the base end surface of the valve 4 to prevent the valve 4 from being detached is attached to the escape hole 35. The retaining member of this embodiment absorbs the dimensional variation of each part and adjusts the base end surface of the valve 4. Hold down spring 37
And a stopper 38 for detachably engaging the retaining groove 36 of the escape hole 35 and stopping the pressing spring 37. A plate-shaped leaf spring is used for the holding spring 37, and a C-shaped ring is used for the stopper 38.

The lifter bridge 20 is not limited to a specific shape as long as it is formed in a bridge shape as described above. In the illustrated example, the lifter bridge 20 is a flat rectangular piece having substantially the same length as the diameter of the end wall 12 in the bridge width direction. And two lifter bodies 1
Two pressing portions 22 disposed on one end wall 12 are formed in a flat rectangular block shape having substantially the same length as the diameter of the end wall 12 in the bridge width direction and located between the two lifter bodies 11. Central part 21 and 1/4 to 2 / of the diameter of end wall 12
3 and two arms 23 connecting between each pressing portion 22 and the central portion 21. Since the pressing portion 22 is formed as long as possible in the bridge width direction (substantially the same length as the diameter of the end wall 12), the depression is effective, and the lifter bridge 20 is hard to fall.

A columnar convex portion 14 provided at the center of the outer surface (upper surface) of each end wall 12 and a concave portion 24 (a through hole in this example) provided at an intermediate portion of each pressing portion 22. The two lifter bodies 11 and the lifter bridge 20 are engaged with each other to prevent the lifter bridge 20 from rotating and falling with respect to the three-dimensional cam 2. Also,
Since the convex portion 14 and the concave portion 24 are fitted to be rotatable relative to each other, the lifter main body 11 can be rotated little by little about its own central axis with vertical reciprocation described later. That is,
The lifter bridge 20 is prevented from rotating by engaging with each lifter main body 11 so as not to hinder the rotation of each lifter main body 11.

Two guide holes 8 are formed in the cylinder head 7, and the guide holes 8 are formed on the peripheral wall 13 of each lifter main body 11.
Guides up and down sliding. Also, two guide holes 8
The lifter bridge 20 (the central portion 2 in the illustrated example)
A recess 8a is formed to allow the reciprocating motion of 1).

A follow-up contact mechanism configured as follows is provided at the central portion 21 of the lifter bridge 20. A semi-cylindrical inner seat 26 extending in the same direction as the axis of the three-dimensional cam 2 is recessed on the upper surface of the central portion 21. Both ends of the semi-cylindrical inner surface seat 26 are open so as to penetrate, and an engagement recess 27 is provided at a substantially central portion in the longitudinal direction of the seat 26.

The semi-cylindrical inner seat 26 includes a semi-cylindrical surface 31 that oscillates (rolls slide) on the seat 26 and a substantially flat contact surface 32 that contacts the three-dimensional cam 2. A cylindrical follow contact portion 30 is fitted so as to be able to roll. A semi-cylindrical surface 31 is integrally provided with a sector-shaped engaging projection 33 at the center in the longitudinal direction, and the engaging projecting part 33 is engaged with the engaging recess 27 and is swingably sandwiched therebetween. With this engagement, in a state where the longitudinal end face of the following contact portion 30 appears,
The movement of the following contact portion 30 in the longitudinal direction is restricted.

The follow contact portion 30 is configured such that the contact surface 32 comes into contact with the three-dimensional cam 2 while swinging at a small angle and following the change in the contact line angle accompanying the rotation of the three-dimensional cam 2. At this time, the three-dimensional cam 2 slidably contacts the contact surface 32 of the following contact portion 30 in the longitudinal direction. However, since the following movement of the following contact portion 30 is restricted as described above, the following contact portion 30 It does not come off the semi-cylindrical inner seat 26.

According to the present embodiment configured as described above, the number of the three-dimensional cams 2 is half the number of the valves 4,
The three-dimensional cam 2 having a large cam width can be formed on the camshaft 1. Therefore, the rate of change of the cam profile in the three-dimensional cam 2 in the axial direction can be moderated,
The displacement of the camshaft can be increased. Therefore, this variable valve mechanism can easily perform continuous variable control by the displacement of the camshaft 1 and can be applied to an internal combustion engine having a multi-valve structure. In addition, since the cylindrical cup-shaped lifter main body 11 can be used, the processing of the lifter main body 11 and the guide hole 8 is easy, and the productivity is improved and the accuracy is easily improved.

Incidentally, since the lifter bridge 20 having the follow-up contact portion 30 is added above the lifter main body 11, the total height of the valve operating mechanism is increased by the lifter bridge 20. However, in the present embodiment, the end wall 1 of the lifter main body 11 is
2 is provided with a retainer structure comprising a cotter fitting portion 17 and a spring seat portion 18, so that a retainer 50 independent of the valve 4 as in the conventional example shown by a two-dot line in FIG.
The total height of the valve mechanism is reduced as shown by the arrow in FIG. Therefore, it is possible to suppress an increase in the overall height of the valve train as a whole, and to improve the mountability to the internal combustion engine. Further, an increase in the valve train mass can be suppressed by the amount that the independent retainer 50 is not required, and high-speed followability can be ensured.

Further, in the present embodiment, the base end of the valve 4 enters the escape hole 35 provided in the end wall 12 and the projection 14 thereof, so that the effect of suppressing the increase in the overall height is high.

Also, the two pressing portions 22 of the lifter bridge 20 are provided with the recesses 24 on the end wall 12 of each lifter main body 11.
The structure of the lifter bridge 20 with respect to the three-dimensional cam 2 is prevented from rotating and falling, and the semi-cylindrical inner surface seat 26 and the follow-up contact part with respect to the rotating direction of the three-dimensional cam 2 are prevented by the simple structure in which the three-dimensional cam 2 is engaged by fitting. Since the direction of 30 does not change, there is no possibility that a load is applied to the valve 4 in the bending direction, and the reliability is improved. In addition, since the convex portion 14 and the concave portion 24 are fitted to be rotatable relative to each other, the lifter main body 11 can be rotated little by little about its own central axis with vertical reciprocation described later. For this reason, the lifter body 11
In addition, uneven wear of the guide hole 8 can be prevented.

The variable valve mechanism according to the present embodiment operates as follows. First, when the internal combustion engine is running at a low speed, the camshaft 1 is displaced leftward by the displacement device as shown in FIG. 4, and the right low-speed cam profile of the three-dimensional cam 2 corresponds to the following contact portion 30. . Then, FIG.
As shown in (b), the follow-up contact part 30 is the one of the three-dimensional cam 2.
It swings by a small angle every rotation, contacts the three-dimensional cam 2 while following the change in the contact line angle, and is pressed by the nose portion 2b.
This pressure is transmitted to the upper surfaces of the end walls 12 of the two lifter bodies 11 via the lifter bridge 20 and the pressing portions 22 thereof, and the two lifter bodies 11 reciprocate up and down based on the low rotation cam profile. Is opened and closed with a small valve opening angle and lift to increase low-speed torque,
Improve fuel economy.

Here, since a force is applied to the valve 4 in a direction in which the cotter 3 comes off by an amount corresponding to the inertia force of the valve 4, the pressing spring 37 having a load corresponding to the inertia force is applied to the stopper ring 3.
8 and the base end surface of the valve 4 is held by the holding spring 37. The base end surface of the valve 4 may be rigidly held by the stopper ring 38 without the holding spring 37. However, in order to absorb the dimensional variation of each part, the holding spring 37 is used.

When the internal combustion engine rotates at high speed, the camshaft 1 is displaced rightward by the displacement device as shown in FIG. Corresponding to Then, FIG.
As shown in (b), the follow-up contact part 30 is the one of the three-dimensional cam 2.
It swings by a small angle every rotation, contacts the three-dimensional cam 2 while following the change in the contact line angle, and is pressed by the nose portion 2b.
Therefore, the lifter bridge 20 and the two lifter bodies 11
Reciprocates up and down based on the cam profile for high rotation, opens and closes each valve 4 at a large valve opening angle and lift amount, increases the intake air amount, and increases the high-speed output.

During the period from the low rotation to the high rotation, the camshaft 1 is continuously displaced by the displacement device in accordance with the operating conditions such as the rotation speed and the accelerator opening, and the three-dimensional cam 2 The cam profile of the intermediate portion corresponds to the following contact portion 30. Accordingly, the lifter bridge 20 and the two lifter bodies 11 reciprocate up and down based on their cam profiles, open and close each valve 4 at an intermediate valve opening angle and lift amount, and provide torque and output according to the operating conditions. Generate.

As described above, according to the variable valve mechanism of this embodiment, the valve timing and the lift amount are continuously changed from the time of low rotation to the time of high rotation of the internal combustion engine, and the operating condition of the internal combustion engine is changed. , And various characteristics such as torque, output, fuel efficiency, and cleanliness of exhaust gas can be maximized over the entire rotation range.

FIGS. 6 and 7 show a variable valve mechanism according to a second embodiment, in which a retaining member is locked in a locking groove 36 of a relief hole 35 and a dimensional variation of each part is absorbed. The second embodiment differs from the first embodiment only in that it is constituted only by a pressing spring 39 for pressing the base end face of the valve 4, and the others are substantially common. A curved strip-shaped leaf spring is used as the pressing spring 39, and ear portions 39a to be locked in the locking grooves 36 are formed at both ends thereof.

Next, FIG. 8 shows a variable valve mechanism according to the third embodiment, in which the uneven portion 4a provided near the base end of the valve 4 and the uneven portion 3a provided on the inner surface of the cotter 3 are different from each other. The second embodiment differs from the first embodiment only in that it is engaged with a clearance for absorbing a dimensional variation of each part in a direction perpendicular to the axis of the first embodiment, and the others are substantially common.

In the first embodiment, the valve 4, the cotter 3, and the lifter body 11 are rigidly fitted to each other, and the guide hole 8 of the cylinder head 7 and the shaft hole (not shown) for guiding the valve 4 are formed. Although it is necessary to increase the coaxial accuracy, the third embodiment has an advantage that the coaxial accuracy may be slightly lower.

Note that the present invention is not limited to the configuration of the above-described embodiment, and may be embodied with the following modifications without departing from the spirit of the invention. (1) The cotter fitting portion 17 is projected outside the end wall. (2) The shape of the holding spring 37 or the stopper 38 is appropriately changed.

[0043]

Since the variable valve mechanism of the present invention is configured as described above, the number of three-dimensional cams can be reduced and the cam width can be increased to facilitate control of various characteristics over the entire rotation range. In addition, it is possible to improve the workability of the valve lifter and the cylinder head, thereby improving the productivity and accuracy, and further, to prevent the valve lifter from being unevenly worn.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a variable valve mechanism according to a first embodiment of the invention.

FIG. 2 is an exploded perspective view of the variable valve mechanism.

FIG. 3 is a sectional view of the variable valve mechanism.

FIG. 4 is a sectional view showing the variable valve mechanism when the internal combustion engine is running at a low speed.

FIG. 5 is a cross-sectional view showing the variable valve mechanism when the internal combustion engine is rotating at a high speed.

FIG. 6 is an exploded perspective view showing a variable valve mechanism according to a second embodiment.

FIG. 7 is a sectional view of the variable valve mechanism.

FIG. 8 is a cross-sectional view illustrating a variable valve mechanism according to a third embodiment.

[Explanation of symbols]

 Reference Signs List 2 solid cam 3 cotter 3a uneven part 4 valve 4a uneven part 6 valve spring 10 direct-acting valve lifter 11 lifter body 12 end wall 13 peripheral wall 14 convex part 17 cotter fitting part 18 spring seat part 20 lifter bridge 21 central part 22 pressing part 23 Arm 24 Concave part 30 Following contact part 35 Escape hole 36 Locking groove 37 Pressing spring 38 Stopper 39 Acquisition spring 39a Ear part

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 13/02 F02D 13/02 H (72) Inventor Tomiho Hirano 10 Hamadashita, Nakahata-cho, Nishio-shi, Aichi Prefecture (72) Inventor Yoshito Moriya 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Hiroyuki Kawase 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72 ) Inventor Koichi Shimizu 1 Toyota Town, Toyota City, Aichi Prefecture F-term in Toyota Motor Corporation (reference) 3G016 AA02 AA05 AA19 BA03 BA19 BA35 BB04 CA04 CA06 DA01 DA22 GA02 3G018 BA04 CA18 DA15 DA17 EA02 EA11 EA31 EA32 FA01 FA06 FA07 GA02 GA17 GA23 3G092 AA11 DA01 DA02 DA04 DA14 DG05 EA01 EA02 FA06 FA36 FA49 HA06Z HE01Z

Claims (11)

[Claims] 1. A three-dimensional cam in which a cam profile is continuously changed in an axial direction from a low-rotation cam profile to a high-rotation cam profile, and the three-dimensional cam is rotated in accordance with an operating condition such as a rotation speed of an internal combustion engine. A direct-acting valve lifter comprising: a displacement device for displacing in the direction; and a direct-acting valve lifter that opens and closes a valve by reciprocating based on a cam profile of the three-dimensional cam. Two or more lifter bodies having a cylindrical peripheral wall, and a bridge portion including a pressing portion for pressing an end wall of each lifter body and a central portion located substantially at the center with respect to each pressing portion are provided. A lifter bridge that is prevented from rotating by engaging with each lifter body, and is provided on the lifter bridge to follow a change in a contact line angle accompanying rotation of the three-dimensional cam. And a follow-up contact mechanism including a follow-up contact portion that contacts the three-dimensional cam, and is fitted to a cotter engaged with a proximal end portion of the valve near an end wall of each lifter main body, and one end of a valve spring is attached to the lifter body. A variable valve mechanism having a retainer structure for receiving the same. 2. A cotter fitting portion provided at a central portion inside each end wall and fitted to a cotter, and a retainer structure portion provided at a circumferential portion inside each end wall and one end of a valve spring. The variable valve mechanism according to claim 1, further comprising a spring seat receiving the spring. 3. The variable valve mechanism according to claim 1, wherein a relief hole into which a base end of the valve enters is provided in the end wall. 4. The variable valve mechanism according to claim 3, wherein a retaining member for pressing a base end face of the valve to prevent the valve from being removed is attached to the escape hole. 5. The retaining member according to claim 4, wherein the retaining member comprises a pressing spring for absorbing a dimensional variation of each part and pressing the base end surface of the valve, and a stopper for stopping the pressing spring by engaging with a relief hole. Variable valve mechanism. 6. The variable valve mechanism according to claim 4, wherein the retaining member comprises a retaining spring that is engaged with the relief hole and absorbs a dimensional variation of each part to press the base end surface of the valve. 7. The valve according to claim 1, wherein the portion near the base end of the valve and the cotter are engaged with a clearance in a direction perpendicular to the axis of the valve to absorb a dimensional variation of each portion. 3. The variable valve mechanism according to claim 1. 8. The engagement between the lifter main body and the lifter bridge is achieved by fitting a convex portion provided on the outside of each end wall with a concave portion provided on each pressing portion. The variable valve mechanism according to claim 1. 9. The variable valve mechanism according to claim 8, wherein the convex portion and the concave portion are fitted so as to be relatively rotatable so as not to hinder the rotation of each lifter body around the central axis. 10. A follow-up contact mechanism comprising a semi-cylindrical inner seat provided at a central portion of the lifter bridge, and a follow-up contact portion fitted to the semi-cylindrical inner seat so as to be able to roll. The variable valve mechanism according to any one of the above. 11. A valve actuating mechanism, wherein a retainer structure for receiving one end of a valve spring and being fitted to a cotter engaged near a base end of a valve is provided on an end wall of the lifter main body. .