Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2002-04-03
2003-02-18
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090190
Reexamination Certificate
active
06520132
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a valve timing control system for controlling open/close timing of an intake valve and/or an exhaust valve, in accordance with operating condition of an internal combustion engine.
2. Description of the Related Art
U.S. Pat. No. 5,832,887 {equivalent of Japanese Patent Unexamined Publication No. Heisei 10 (1998)-110603} discloses a valve timing control system (referred to as “rotational phase adjusting apparatus” in the above Publication) for variably controlling open/close timing of an intake valve or an exhaust valve of an internal combustion engine. The above variable control is carried out by rotating an angle of a drive force conveyer (including a timing pulley, a chain sprocket and the like synchronously rotating with a crank shaft of the internal combustion engine) relative to a cam shaft (having an outer periphery formed with a drive cam).
The valve timing control system disclosed in U.S. Pat. No. 5,832,887 has a housing on a side defining the drive force conveyer. A vane rotor is integrated with an end of the cam shaft, and is housed in the housing. Also housed in the housing are an advanced angle chamber and a retarded angle chamber. Supplying an oil pressure to and draining the oil pressure from each of the advanced angle chamber and the retarded angle chamber allows the vane rotor to rotate relative to the housing, to thereby vary a rotational phase of the drive force conveyer relative to the cam shaft. With this, the open/close timing of the intake valve or the exhaust valve of the internal combustion engine is controlled.
Moreover, for improving startability of the internal combustion engine, overlap of the intake valve with the exhaust valve is to be reduced. Therefore, the valve timing control system according to U.S. Pat. No. 5,832,887 is provided with a lock gear which mechanically locks, during engine stop, the vane rotor and the housing at an angle where the overlap is minimized (for the intake valve, a most retarded angle; while for the exhaust valve, a most advanced angle).
More specifically, as is seen in
FIG. 10
, a vane rotor
1
has a vane section which is provided with a lock pin
2
moving forward and backward (respectively, leftward and rightward in FIG.
10
). A spring
3
biases lock pin
2
in a direction of protrusion (leftward in FIG.
10
). On the other hand, on a side having a housing
5
, there is defined a lock hole
4
which mates with lock pin
2
at an initial position (where the overlap of the intake valve with the exhaust valve is minimized). Therefore, returning vane rotor
1
to the initial position during the engine stop allows lock pin
2
to protrude, with a biasing force applied to lock pin
2
from spring
3
. With this, a head end (left end in
FIG. 10
) of lock pin
2
engages with lock hole
4
.
Furthermore, the valve timing control system according to U.S. Pat. No. 5,832,887 is provided with an unlock gear for unlocking, after the start of the internal combustion engine, the lock condition by the lock gear. The unlock gear allows the oil pressure of each of the advanced angle chamber and the retarded angle chamber to act on lock pin
2
for the unlocking. More specifically, on a side having vane rotor
1
, a pin hole
6
for receiving lock pin
2
is in a form of a two-step hole, namely, constituted of a small diameter hole
6
a
and a large diameter hole
6
b
. On the other hand, the lock pin
2
is constituted of a small diameter section
2
a
and a large diameter section
2
b
. Small diameter section
2
a
is disposed at the head end (left in
FIG. 10
) of lock pin
2
, for mating in and coming out of small diameter hole
6
a
. Large diameter section
2
b
is larger than small diameter section
2
a
, and in a form of a flange. Large diameter section
2
b
is received in large diameter hole
6
b
at a bottom end (right in FIG.
10
).
The oil pressure of one of the advanced angle chamber and the retarded angle chamber is supplied to the base (left in
FIG. 10
) of lock hole
4
. Contrary to this, the oil pressure of the other of the advanced angle chamber and the retarded angle chamber is supplied to an annular space
7
which is defined between a stepped face {formed between large diameter hole
6
b
and small diameter hole
6
a
(of pin hole
6
)} and large diameter section
2
b
(of lock pin
2
).
When the oil pressure of one of the advanced angle chamber and the retarded angle chamber is increased, with lock pin
2
engaging with lock hole
4
(lock condition), the oil pressure acts against the force of spring
3
in such a manner as to move lock pin
2
backward (rightward in FIG.
10
).
In the valve timing control system according to U.S. Pat. No. 5,832,887, when the relative rotation of vane rotor
1
and housing
5
reaches the initial position, lock pin
2
is to assuredly engage with lock hole
4
. It is difficult, however, to completely align pin hole
6
and lock hole
4
on an axis at the initial position.
In other words, for aligning pin hole
6
and lock hole
4
on the axis at the initial position; production accuracy/precision and assembly accuracy/precision of housing
5
and vane rotor
1
are increased, likewise, machining accuracy/precision and the like of pin hole
6
and lock hole
4
are increased. Increasing the accuracy/precision as described above is not feasible with the present technology.
Thereby, according to U.S. Pat. No. 5,832,887, small diameter hole
6
a
is larger than small diameter section
2
a
, while large diameter hole
6
b
is larger than large diameter section
2
b
. Moreover, according to U.S. Pat. No. 5,832,887, a clearance d is so defined between lock pin
2
and pin hole
6
as to absorb an axial shift of pin hole
6
from lock hole
4
.
According to U.S. Pat. No. 5,832,887, however, the clearance d is common in dimension to the following two:
1. between small diameter section
2
a
and small diameter hole
6
a
, and
2. between large diameter section
2
b
and large diameter hole
6
b
.
Thereby, allowing the oil pressure (for unlocking) to act on lock pin
2
when lock pin
2
engages with pin hole
6
with an inclination causes an edge E of large diameter section
2
b
to abut on an inner periphery of large diameter hole
6
b
, as is seen in
FIG. 10
(partly enlarged area). The abutment of edge E may prevent smooth removal of lock pin
2
from pin hole
6
.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a valve timing control system for an internal combustion engine.
It is another object of the present invention to provide the valve timing control system having a lock pin which assuredly engages with a lock hole at an initial position (where an overlap of an intake valve with an exhaust valve is minimized), and achieving a smooth unlocking operation.
It is still another object of the present invention to allow the valve timing control system to have a vane rotor which is free from causing flapping at the initial position, and to smoothen rotational phase variation.
According to a first aspect of the present invention, there is provided a valve timing control system of an internal combustion engine. The valve timing control system comprises:
a drive force conveyer driven by a crank shaft of the internal combustion engine;
a cam shaft having an outer periphery formed with a drive cam for driving a valve of the internal combustion engine, the drive force conveyer being mounted to the cam shaft in such a manner as to make a rotation relative to the cam shaft when so requested, the cam shaft receiving a drive force from the drive force conveyer to rotate as a follower;
a housing rotating integrally with one of the drive force conveyer and the cam shaft;
a vane rotor housed in the housing, the vane rotor rotating integrally with the other of the drive force conveyer and the cam shaft;
an advanced angle chamber and a retarded angle chamber housed in the housing, and turning the vane rotor with an oil pressure;
an oil pressure supply-drain
Lo Weilun
Unisia Jecs Corporation
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