Internal-combustion engines – Poppet valve operating mechanism
Reexamination Certificate
1999-07-12
2001-04-24
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
Reexamination Certificate
active
06220209
ABSTRACT:
The disclosure of Japanese Patent Application No. Hei. 10-234233 filed on Aug. 20, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a rocking follower mechanism for a three-dimensional cam. In particular, the invention relates to a rocking follower mechanism for a three dimensional cam for transmitting a positional variation of a cam surface of a three-dimensional cam to a valve lifter, in response to revolutions of an internal combustion engine.
2. Description of Related Art
There is a known variable valve timing mechanism capable of varying the on-off timing of an intake valve or an exhaust valve of an internal combustion engine. This is performed in accordance with operation of an internal combustion engine. In one of such variable valve timing mechanisms, there is a known mechanism as shown in
FIG. 10. A
lift amount of a valve
103
is varied using a three-dimensional cam
102
movable in the rotational axial direction so as to adjust the on-off timing of the valve, as disclosed in Japanese Patent Application Laid-open No. Hei 10-196333, for example.
In such a variable valve timing mechanism using a three-dimensional cam, a tilt angle of a cam surface
102
a
varies with the rotation. Also, a guide groove
105
, extending in parallel with the rotational direction of the three-dimensional cam
102
, is formed in the top surface
104
a
of a valve lifter
104
. A semi-columnar follower
106
is capable of rocking in accordance with variation in the tilt angle of the cam surface
102
a
. The follower
106
is disposed in the guide groove
105
such that the three-dimensional cam
102
is sufficiently brought into contact with the valve lifter
104
. This results in enhanced durability.
Further, in such a structure, the cam surface
102
a
of the three dimensional cam
102
slides on a cam sliding surface of the semi-columnar follower
106
in the axial direction thereof. Therefore, as shown in
FIG. 10
, the semi-columnar follower
106
has a wide portion
106
b
formed at its center. The guide groove
105
also has a wide groove
105
a
formed therein into which the wide portion
106
b
is inserted. The above described structure may allow a thrust surface
106
c
of the wide portion
106
b
to abut against a thrust surface
105
b
of the expanded- width groove
105
a
. As a result, the axial movement of the follower
106
is suppressed against the sliding movement of the cam surface
102
a.
However, the wide portion
106
b
, formed in the center of the follower
106
, is required to have a cam sliding surface
106
d
. The cam sliding surface
106
d
radially extends from the cam sliding surface
106
a
of the follower
106
, on which the three-dimensional cam
102
slides.
The cam surface
102
a
of the three-dimensional cam
102
varies its position in contact with the cam sliding surface
106
a
, of the follower
106
, by moving along a shaft
107
axially. As a result, the lift amount of the valve
103
is varied. Therefore, a width Cw of the cam surface
102
a
, in the axial direction, is greater than a width Fw of the cam sliding surface
106
a
of the follower
106
.
Further, the sliding position between the cam surface
102
a
, of the three-dimensional cam
102
, and the sliding surface
106
a
, of the follower
106
, always varies in the axial direction of the follower
106
(in the direction of the arrow Z in FIG.
10
). This variance is in response to the rotation of the three-dimensional cam
102
.
Therefore, the cam surface
102
a
, of the three dimensional cam
102
, slides so as to move along a portion defined by the cam sliding surface
106
a
, that is not adjacent to the cam sliding surface
106
d
of the wide portion
106
b
, and the cam sliding surface
106
a
, which is adjacent to the cam sliding surface
106
d
. If the sliding position is moved, the cam surface
102
a
of the three-dimensional cam
102
collides against an angular portion
106
e
. The angular portion
106
e
is defined by the thrust surface
106
c
and the cam sliding surface
106
d
of the wide portion
106
b.
The aforementioned collision is likely to generate a hit sound. As may be appreciated, this sound is not preferable in view of driving environment of a motor vehicle, for example. Further, the collision may cause abrasion on the cam surface
102
a
, of the three-dimensional cam
102
, as well as the cam sliding surface
106
d
of the wide portion
106
b
. This abrasion is heavy in comparison with the abrasion caused by the normal sliding movement. Accordingly, such abrasion resulting from the collision is not preferable in view of the durability of the variable valve timing mechanism.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a follower capable of preventing the generation of a hit sound without causing excessive abrasion on the follower itself, as well as a cam surface of a three-dimensional cam, while providing the wide portion in the follower for preventing the axial movement.
To achieve the above object, the present invention provides a rocking follower mechanism for a three-dimensional cam. A guide groove is formed on a valve lifter of an internal combustion engine having a wide groove on at least a portion thereof. A rocking follower is supported in the guide groove. The rocking follower has a cam sliding surface that is brought into contact with a cam surface of the three-dimensional cam. The three-dimensional cam has different profiles in the axial direction such that a positional variation of the cam surface, in accordance with the rotation of the internal combustion engine, is transmitted to the valve lifter. The rocking follower includes a wide portion corresponding to the expanded width groove of the guide groove for accommodating the wide portion. As a result, the rocking follower is prevented from moving in a direction of the rocking axis. A wide portion is formed at a position in the rocking follower so as not to be in contact with the cam surface.
Accordingly, the wide portion of the rocking follower is positioned so as not to be in contact with and slide on the cam surface of the three-dimensional cam. As a result, the cam surface does not abut against the surface or the angular portion of the wide portion. Therefore, excessive abrasion is not generated on the cam surface of the three-dimensional cam and the rocking follower itself. Further, the hit sound as described above can also be prevented.
In accordance with the invention, among surfaces of the wide portion, the surface facing the three-dimensional cam may be formed closer to the valve lifter than the cam sliding surface.
With the structure described above, the surface of the expanded edge portion opposing the three-dimensional cam is formed closer to the valve lifter than the cam sliding surface. As a result, the cam surface of the three-dimensional cam is not brought into contact with the surface of the wide portion. Therefore, this arrangement prevents collision of the cam surface of the three-dimensional cam against the surface of the wide portion or the angular portion defined by the thrust surface thereof.
In addition, among surfaces of the wide portion, a top of the surface facing the three-dimensional cam may be formed as a tilting surface toward the valve lifter.
The top of the surface of the wide portion opposing the three-dimensional cam may be formed as the tilting surface toward the valve lifter. As a result, it is possible to prevent the cam surface of the three-dimensional cam from contacting with the surface of the wide portion. Therefore, collision of the cam surface of the three-dimensional cam against the surface of the wide portion or the angular portion defined by the thrust surface can be avoided.
REFERENCES:
patent: 5803033 (1998-09-01), Naruoka
patent: 5806477 (1998-09-01), Regueiro
patent: 5832889 (1998-11-01), Naruoka et al.
patent: 5988127 (1999-11-01), Hasegawa et al.
Kikuoka Shinichiro
Moriya Yoshihito
Nagaosa Hideo
Nakano Shuuji
Oliff & Berridg,e PLC
Patel Vinod D.
Toyota Jidosha & Kabushiki Kaisha
Walberg Teresa
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