Variable valve lift device

Details Variable valve lift device Variable valve lift device

2002-03-11

2004-05-04

Denion, Thomas (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090150, C123S090480, C074S569000

Reexamination Certificate

active

06729282

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable valve lift device used for a direct drive-style valve driving system driving directly an intake or exhaust valve (hereafter, referred as a valve) using a cam when the valve of an internal combustion engine (hereafter, referred as an engine) is opened and closed. The variable valve lift device (hereafter, referred as a VVL device) changes a length of a tappet in an axial direction to adjust a valve lift of the valve.
2. Description of the Prior Art
With a conventional rocker arm-style engine, in order to adjust the valve lift of the valve responsive to any operational status of the engine, cam-profiles arranged on a camshaft, each profile corresponding to a required valve lift, and a switching mechanism is arranged in the rocker arm. With such a constructed engine, it is necessary to arrange the plurality of cam profiles on the camshaft and accordingly to increase the cost of manufacture. It further runs counter to a request of reduction in weight.
On the other hand, in recent years, the direct drive-style engine driving directly the valve using a cam without using the rocker arm provides with the VVL device adjusting the valve lift of the valve responsive to any operational status of the engine. A known VVL device includes a tappet case arranged between the cam and the valve and a variable valve lift system built into the tappet case. Construction regarding a general direct drive-style engine and the conventional VVL device will be described in detail hereafter.
FIG. 1
is a diagrammatic sketch of direct drive-style valve driving system in the engine.
FIG. 2
is a view taken in the direction of arrow A—A in FIG.
1
and showing a cam on a camshaft in the valve driving system.
FIG. 3
is a front view of a cam-profile of a cam shown in FIG.
2
. Here, only an intake valve driving system of the intake and exhaust valve driving systems is indicated. Since the exhaust valve driving system has the same construction as the intake valve driving system, the exhaust valve driving system is also operated by the same action as the intake valve driving system. Therefore, further description will be omitted. Moreover, assume that a cylinder shown in the drawing is arranged in a vertical direction.
In the drawings, reference numerals
1
,
2
,
3
and
4
denote cylinders in a four-cylinder engine. Pistons
5
,
6
,
7
and
8
are arranged in the respective cylinders
1
,
2
,
3
and
4
, each reciprocating in an axial direction of each cylinder. Reciprocal movements of the pistons
5
,
6
,
7
and
8
are converted into rotational movements and transferred to a crankshaft
13
. Two valve seats
14
,
15
,
16
and
17
per cylinder are arranged at an upper section (cylinder head) of the cylinders
1
,
2
,
3
and
4
, respectively. Intake valves
18
,
19
,
20
and
21
are arranged at the valve seats
14
,
15
,
16
and
17
, respectively. Rotational movements of intake cams
26
,
27
,
28
and
29
are transferred to the intake valves
18
,
19
,
20
and
21
byway of a VVL devices
22
,
23
,
24
and
25
. The intake cams
26
,
27
,
28
and
29
are arranged on an intake camshaft
30
. The intake camshaft
30
can be rotated in a direction of arrow B in
FIG. 2
due to a rotational driving force of the crankshaft transferred to the intake camshaft
30
via a pulley
31
, a driving force transferable member
32
such as timing belts, and a pulley
33
.
Here, since all the intake cams
26
,
27
,
28
and
29
have the same construction, the intake cam
26
will be explained as a representative example. The intake cam
26
shown in
FIG. 3
includes a base-circle section
26
a
having a circular-shape in cross section, a lift-curve section
26
b
protruded from the base-circle section
26
a
and two ramp sections
26
c
and
26
d
connecting smoothly the base-circle section
26
a
to the lift-curve section
26
b
and vice versa. Another intake cams
27
,
28
and
29
have the construction above as in the case of the intake cam
26
.
The lift-curve section
27
b
of the intake cam
27
and the lift-curve section
28
b
of the intake cam
28
are shifted plus or minus 90 degrees with respect to the lift-curve section
26
b
of the intake cam
26
in an outer periphery of the intake camshaft
30
as shown in FIG.
2
. The lift-curve section
29
b
of the residual intake cam
29
is shifted approximately 180 degrees with respect to the lift-curve section
26
b
of the intake cam
26
in an outer periphery of the intake camshaft
30
.
Here, since all the VVL devices
22
,
23
,
24
and
25
have the same construction, the VVL device
22
will be explained as a representative example. The conventional VVL device
22
has a construction as disclosed in German Patent Gazette DT1958627. The conventional VVL device
22
includes a tappet case
34
having an upper section with a cam contact section
34
a
making contact with a cam face of the intake cam
26
. The device
22
includes a hydraulic cylinder (not shown) arranged in the tappet case
34
to select a high-lift mode extending the length of the tappet in the axial direction and a low-lift mode shrinking it.
A lower section of the VVL device
22
makes contact with an upper section of a valve stem
35
. The intake valve
18
is mounted on a lower section of the valve stem
35
. A valve spring (not shown) is arranged between the valve stem
35
and the cylinder
1
and biases upwardly the valve stem
35
in the axial direction to press the intake valve
18
against the valve seat
14
to close it.
An operation of the VVL device
22
will be explained hereafter.
First, just after the engine is started, a hydraulic pressure supplied from an oil pump (not shown) to the VVL device
22
does not yet rise to adequate levels and the hydraulic cylinder (not shown) in the VVL device
22
is not extended. Therefore, the hydraulic cylinder (not shown) is so set as to select the low-lift mode. With the low-lift mode, when the intake cam
26
rotates in the direction of arrow B in
FIG. 2
, the cam contact section
34
a
of the tappet case
34
makes contact with the intake cam
26
to run from the base-circle section
26
a
to the lift-curve section
26
b
via the ramp section
26
c
. However, a downward displacement of the cam contact section
34
a
in the axial direction is not yet increased. Therefore, the tappet case
34
and the valve stem
35
do not move downwardly in the axial direction. When the intake cam
26
further rotates, the cam contact section
34
a
of the tappet case
34
makes contact with the intake cam
26
to run from the ramp section
26
c
to a middle of the lift-curve section
26
b
. At this time, the downward displacement of the cam contact section
34
a
in the axial direction is increased. Therefore, the tappet case
34
and the valve stem
35
are pressed down against the biasing force of the valve spring (not shown) and the intake valve
18
also is pressed down in the axial direction with respect to the valve seat
14
(low-lift state).
Moreover, when the engine is driven usually, the hydraulic pressure supplied from an oil pump (not shown) to the VVL device
22
rises to adequate levels and the hydraulic cylinder (not shown) in the VVL device
22
is extended. Therefore, the hydraulic cylinder (not shown) is so set as to select the high-lift mode. With the high-lift mode, when the intake cam
26
rotates in the direction B in
FIG. 2
, the cam contact section
34
a
of the tappet case
34
makes contact with the intake cam
26
to run from the base-circle section
26
a
to the lift-curve section
26
b
in orderly sequence. However, a downward displacement of the cam contact section
34
a
in the axial direction is not yet increased. Therefore, the tappet case
34
and the valve stem
35
do not move downwardly in the axial direction. When the intake cam
26
further rotates, the cam contact section
34
a
of the tappet case
34
makes contact with the intake cam
26
to run from the base-circle section
26
a
to

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