Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
1999-07-14
2001-06-12
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090280, C123S090500
Reexamination Certificate
active
06244229
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-251284 filed on Sep. 4, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a valve lifter for a three-dimensional cam used in an internal combustion engine and a variable valve operating apparatus using the valve lifter.
2. Description of the Related Art
There is a known variable valve operating apparatus capable of varying the timing for opening and closing an intake valve or an exhaust valve of an internal combustion engine in accordance with a driving state of the internal combustion engine. As one example of the variable valve operating apparatus, there is a known apparatus for adjusting the opening and closing timing of a valve by varying the lift amount of a valve
1003
using a three-dimensional cam
1002
capable of moving in a direction of a rotation axis as shown in
FIG. 38
(Japanese Patent Application Laid-Open No. HEI 10-121926).
In the variable valve operating apparatus using such a three-dimensional cam, the incline angle of a cam surface
1002
a
is varied as the three-dimensional cam rotates. Therefore, a guide groove
1005
extending in parallel with the rotation direction (direction of the arrow S in the drawing) of the three-dimensional cam is formed on a top surface
1004
a
of a valve lifter
1004
. A semicolumnar rocking follower
1006
capable of rocking in accordance with variation of the incline angle of the cam surface
1002
a
is fitted in the guide groove
1005
for enhancing the durability by maintaining sufficient contact between the three-dimensional cam
1002
and the valve lifter
1004
.
In the aforementioned structure, the cam surface
1002
a
of the three-dimensional cam
1002
applies pressure to the valve lifter
1004
obliquely through the rocking follower
1006
. Therefore, a strong moment acts on the valve lifter
1004
about its axis which is caused to rotate in a lifter bore
1009
a
provided in a cylinder head
1009
of the internal combustion engine. The aforementioned rotation of the valve lifter
1004
may change the direction of the rocking follower
1006
undesirably. Therefore, the valve lifter
1004
is provided with a projection
1004
c
at its outer peripheral surface as a detent mechanism for the valve lifter
1004
such that the projection
1004
c
is brought into engagement with a groove formed in an inner peripheral surface of the lifter bore
1009
a
in its axial direction. This mechanism allows the valve lifter
1004
to slide within the lifter bore
1009
a
in its axial direction but not to rotate, thus maintaining the direction of the rocking follower
1006
.
However, there has been a recent trend to decrease the thickness of the valve lifter
1004
in order to reduce the weight of the internal combustion engine. This may restrict a position for mounting the projection
1004
c
or its shape as well.
For example, as the detent projection cannot be force fitted to the outer peripheral surface
1004
b
as a thin portion, it is necessary to mount the projection by welding that requires more time than the force fitting. When the projection is mounted on the thin portion by welding, the inside thereof may be deformed to give an adverse effect on roundness of the valve lifter
1004
. Further, as a largesized projection cannot be mounted, the surface pressure applied to the groove to be engaged with the projection is increased. It is, thus, probable to threaten deteriorated durability.
A similar problem may be raised when forming a detent groove on the valve lifter
1004
. Since a groove with sufficient depth cannot be formed in the thin portion, the area contacting the projection inserted from the cylinder head is reduced to increase the surface pressure. As A result, a detent mechanism having sufficient durability cannot be obtained.
In order to form the detent projection having sufficient contacting area, there has been no alternative but to mount a small-sized projection on a relatively thick portion near the top surface
1004
a
of the valve lifter. The degree of freedom in the detent mechanism design, thus, is extremely lowered.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the above problems, and it is an object of the invention to enhance durability of the valve lifter for the three-dimensional cam and a variable valve operating apparatus by increasing the degree of freedom design of a detent mechanism of a valve lifter for a three-dimensional cam.
To achieve the above object, according to a first aspect of the invention, there is provided a valve lifter for a three-dimensional cam accommodated in a lifter bore provided in a cylinder head of an internal combustion engine including a cylindrical outer peripheral surface having a projection engaging a groove in the lifter bore formed at least partially for preventing rotation, and an accommodation chamber for accommodating at least a stem end portion of a valve. The center axis of the cylindrical outer peripheral surface and a center axis of the accommodation chamber are offset, and the projection is formed on the outer peripheral surface at a position corresponding to a thick wall portion at which a distance between the outer peripheral surface and the accommodation chamber generated by the offset becomes substantially maximum.
According to the above aspect, a spatial room constituting the thick wall portion can be generated by the offset between the outer peripheral surface of the valve lifter for the three-dimensional cam and the accommodation chamber in which the structure of the stem end portion are accommodated, and thickness of other portions of the valve lifter can be substantially thin. Therefore, the weight as a whole is not increased, or the valve lifter can further be lightened by further reducing the thickness of the portion except the thick wall portion. The projection can be mounted to the thick wall portion using a simple process, such as a force fitting process. Further, a sufficiently large sized projection can be mounted without generating deformation in the valve lifter for the three-dimensional cam. Therefore, the surface pressure acting on the groove in the lifter bore can be reduced, resulting in no possibility of deteriorated durability.
Further, the position for mounting the detent mechanism of the valve lifter for the three-dimensional cam is no longer limited to the location around the top surface, but to the outer periphery, thus increasing the freedom in designing the detent mechanism to the greatest degree.
In the above aspect, the accommodation chamber may have a cylindrical shape, and the thick wall portion may be formed by the offset between the inner peripheral surface of the accommodation chamber and the outer peripheral surface of the cylindrical chamber.
With the structure, the thick wall portion is formed at the portion where the distance between the outer peripheral surface and the accommodation chamber generated by the offset becomes substantially maximum. This may be realized by offsetting the center axes of the outer peripheral surface and the inner peripheral surface of the cylindrical chamber. The accommodation chamber can be made using a simple process, such as forming a cylindrical hole.
In the above aspect, the projection may have an arcuate, convex surface of a given radius of curvature R opposing a side surface of the groove to be engaged.
In the projection of the detent mechanism, since the surface opposing the side surface of the groove has the arcuate shape, when the valve lifter for the three-dimensional cam is cocked, the angled portions of the upper and lower ends of the projection are prevented from contacting the side surface of the opposing groove as compared with a case having the projection with a straight surface. Therefore, it is possible to maintain the contacting surface pressure at a low level to prevent abnormal abrasion, and to enhance durabil
Kikuoka Shinichiro
Moriya Yoshihito
Nagaosa Hideo
Nakano Shuuji
Dahbour Fadi H.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Walberg Teresa
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