Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2002-06-27
2003-07-08
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090480, C123S090550
Reexamination Certificate
active
06588386
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a variable valve lift system. More particularly, the present invention relates to a variable valve lift system in which a valve lift is varied in two stages through changes in valve lift and cam duration by selectively rigidly engaging a tappet shim.
BACKGROUND OF THE INVENTION
An engine is typically structured such that cams mounted on a camshaft open and close intake and exhaust valves by rotation of the camshaft. In some modem engines, a variable valve control system is used in which valve timing and the amount of lift of the valves are controlled to improve performance and reduce fuel consumption.
With reference to
FIGS. 1 and 2
, a conventional variable valve lift system for controlling the degree of valve lift includes a tappet shim
3
that receives operational force from cam
1
, and a body
7
for transmitting an operational force from the tappet shim
3
to a valve
5
. Supports
11
are mounted to four points on the tappet shim
3
and supports
13
are mounted to four points on the body
7
. The four points of the tappet shim
3
oppose the four points of the body
7
. An elastic member
9
is interposed between each opposing pair of supports
11
and
13
to provide a biasing force to the supports
11
in the direction of the tappet shim
3
and a biasing force to the supports
13
in the direction of the body
7
.
Further, stoppers
17
and
19
are mounted in hydraulic pressure chambers
21
and
23
, respectively, of the body
7
. An elastic member
15
is interposed between the stoppers
17
and
19
. The stoppers
17
and
19
move by interaction with the elastic member
15
and with oil in the hydraulic pressure chambers
21
and
23
. Oil holes
25
lead into the hydraulic pressure chambers
21
and
23
to enable the supply of oil thereto.
In the variable valve lift system structured as in the above, if oil is not supplied through the oil holes
25
, the stoppers
17
and
19
are positioned within the hydraulic pressure chambers
21
and
23
, respectively, as a result of receiving a biasing force of the elastic member
15
. As a result, a state in which the tappet shim
3
is not upwardly supported is maintained. Hence, the operational force of the cam
1
, transmitted to the tappet shim
3
, is absorbed by the elastic members
9
positioned between the supports
11
and
13
such that the valve
5
is operated through the body
7
. With such operation, the amount of lift of the valve
5
cannot be varied.
On the other hand, with reference to
FIGS. 3 and 4
, if oil (a) is supplied through the oil holes
25
, the stoppers
17
and
19
overcome the biasing force of the elastic member
15
such that the stoppers
17
and
19
are forced in a direction toward each other to be positioned at the outside edge of the hydraulic pressure chambers
21
and
23
, respectively. As a result, the tappet shim
3
is upwardly supported, that is, the tappet shim
3
cannot be downwardly displaced into the body
7
in this state. Hence, the operational force of the cam
1
, transmitted through the tappet shim
3
, operates the valve
5
through the body
7
after it is transmitted by the supports
11
and
13
and the stoppers
17
and
19
. The amount of lift of the valve
5
is increased as a result.
However, in the above variable lift system, since the two stoppers
17
and
19
support the tappet shim
3
during application of a load by a cam lobe, the stoppers
17
and
19
experience wear. Further, the elastic member
15
, interposed between the stoppers
17
and
19
, does not precisely return the stoppers
17
and
19
when oil is exhausted from the hydraulic chambers
21
and
23
.
SUMMARY OF THE INVENTION
The present invention provides a variable valve lift system in which valve lift is varied in two stages through changes in valve lift and cam duration by selectively rigidly engaging a tappet shim, and in which the durability of the support and the return of the stopper are improved. In a preferred embodiment, a tappet shim receives an operational force from the cam. A body transmits an operational force of the tappet shim to the valve. First and second supports, the first supports being provided on a surface of the tappet shim opposing the body and the second supports being provided on a surface of the body opposing the tappet shim, are supported by elastic members. First and second stoppers, mounted respectively in first and second hydraulic pressure chambers, formed on opposite sides of the body, are provided with an elastic member interposed between the first stopper and the body and an elastic member interposed between the second stopper and the body. The first and second stoppers selectively rigidly support the tappet shim in a second lift stage. A third stopper is mounted in a third hydraulic pressure chamber, which is formed in the body at a location opposing the tappet shim, and an elastic member is interposed between the third stopper and the body.
Preferably, the elastic members positioned in the first, second, and third hydraulic pressure chambers provide a biasing, pulling force to create resistance to hydraulic pressure acting on the first, second, and third stoppers. It is also preferable that the third stopper be mounted at substantially a center portion of the body to support the tappet shim in a state that is balanced during operation under the lobe load of the cam. It is further preferable that the third stopper is further configured to provide a higher position than the first and second stoppers during operation such that the third stopper supports the tappet shim at a high lift of the valve when oil is supplied to the third hydraulic pressure chamber.
REFERENCES:
patent: 5431133 (1995-07-01), Spath et al.
patent: 5709180 (1998-01-01), Spath
patent: 6125804 (2000-10-01), Kawai et al.
Denion Thomas
Hyundai Motor Company
Pennie & Edmonds LLP
Riddle Kyle
LandOfFree
Variable valve lift system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Variable valve lift system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variable valve lift system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3035258