Internal-combustion engines – Poppet valve operating mechanism – Tappet
Reexamination Certificate
2001-09-26
2003-02-18
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Tappet
C123S090160, C123S090170, C123S090520, C123S090550
Reexamination Certificate
active
06520135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for adjusting a valve lift (hereinafter called as a variable valve lifting, VVL, apparatus) which is used in a direct-strike type of valve driving system in which a tappet is directly stricken by a cam when an intake valve or an exhaust valve (hereinafter referred to as a valve altogether) of an internal combustion engine (hereinafter called an engine) is opened or closed, in which an amount of valve lifting (hereinafter called a valve lift amount) is adjusted by changing an axial length of the tappet.
2. Description of the Prior Art
FIG. 24
is a schematic view showing an arrangement of a general valve system of an engine.
FIG. 25
is a view as seen in the direction of arrows A—A showing an arrangement of cams on a camshaft in the valve driving system in FIG.
24
.
FIG. 26
is a front view showing a profile of the cam in FIG.
25
.
FIGS. 27A through 27G
are schematic sectional views to show a conventional valve opening movement and valve closing movement of the VVL apparatus shown in
FIG. 24
in a low lift mode, and
FIG. 27H
is a graph continuously showing the change in the valve lift amount.
FIGS. 28A through 28G
are schematic sectional views to show the conventional valve opening movement and valve closing movement of the VVL apparatus shown in
FIG. 24
in a high lift mode, and
FIG. 28H
is a graph continuously showing the change in the valve lift amount.
In the example given hereinbelow, only the valve driving system on the intake side is shown out of the valve driving system for each of the intake side and the exhaust side. Since the valve driving system on the exhaust side has basically the same arrangement, an explanation thereabout is omitted. In addition, explanations are made hereinbelow based on the presumption that the cylinders in the figures are disposed in a vertical direction.
In the figures, each reference numeral
1
,
2
,
3
,
4
denotes a cylinder of a 4-cylinder engine (hereinafter simply called a cylinder). Inside each of these cylinders
1
,
2
,
3
and
4
, there is disposed a piston
5
,
6
,
7
,
8
which reciprocates in an axial direction of the respective cylinders. The reciprocating movements of these pistons
5
,
6
,
7
and
8
are converted into rotary movements by crank mechanisms
9
,
10
,
11
and
12
for transmission to a crankshaft
13
. On an upper portion (cylinder head) of each of the cylinders
1
,
2
,
3
and
4
, there are provided two valve seats
14
,
15
,
16
and
17
, respectively. An intake valve
18
,
19
,
20
,
21
is disposed in each of the valve seats
14
,
15
,
16
and
17
. The intake valves
18
,
19
,
20
and
21
are arranged to be subject to rotational driving of intake-side cams
26
,
27
,
28
and
29
, respectively, through an apparatus for adjusting a valve lift (hereinafter called a variable valve lifting, VVL, apparatus)
22
,
23
,
24
,
25
. Intake-side cams
26
,
27
,
28
and
29
are disposed on an intake-side camshaft
30
. The intake-side camshaft
30
is rotatable in a direction as shown in
FIG. 25
by an arrow B by a rotational driving force to be transmitted by a drive transmission member
32
such as a pulley
31
, a timing belt, or the like, as well as a pulley
33
.
Here, since the intake-side cams
26
,
27
,
28
and
29
have all the similar construction, an explanation will now be made about the intake-side cam
26
as a typical example. The intake-side cam
26
is made up, as shown in
FIG. 26
, of a base circle section
26
a
of a true circle in cross section, a lift curve section
26
b
which is raised from this base circle section
26
a
, and ramp sections
26
c
and
26
d
which smoothly connect the base circle section
26
a
and the lift cure section
26
b
together. This arrangement is the same as that of the remaining intake-side cams
27
,
28
and
29
.
As shown in
FIG. 25
, the lift curve section
27
b
of the intake-side cam
27
and the lift curve section
28
b
of the intake-side cam
28
are disposed at an offset of about ±90° on the periphery of the intake-side camshaft
30
relative to the lift curve section
26
b
of the intake-side cam
26
. The lift curve section
29
b
of the remaining intake-side cam
29
is disposed at an offset of about 180° on the periphery of the intake-side camshaft
30
relative to the lift curve section
26
b
of the intake-side cam
26
.
Since the above VVL apparatuses
22
,
23
,
24
and
25
have all the similar constructions, an explanation will now be made about the VVL apparatus
22
as a typical example. As shown in
FIGS. 27 and 28
, the VVL apparatus
22
is roughly made up of: a tappet casing
34
having on an upper portion thereof a cam contact portion
34
a
which comes into contact or abutment with a cam surface of the intake-side cam
26
; and a hydraulic cylinder (not illustrated) which is disposed inside the tappet casing
34
and which switches between a high lift mode in which a tappet axial length is extended and a low lift mode in which the tappet axial length is contracted. This arrangement is disclosed in German Patent Publication DT1958627. The lower portion of this VVL apparatus
22
is in contact or abutment with an upper portion of a valve stem
35
. On a lower portion of this valve stem
35
there is provided the above-described intake valve
18
. Between this valve stem
35
and the cylinder
1
there is disposed a valve spring
36
which urges the valve stem
35
axially upward to urge the intake valve
18
against the valve seat
14
, whereby the intake valve
18
is brought into a closed state.
An explanation will now be made about the operation of the VVL apparatus
22
.
First, right after starting the engine, since the hydraulic pressure to be supplied from an oil pump (not illustrated) to the VVL apparatus
22
is not high enough, the hydraulic cylinder (not illustrated) inside the VVL apparatus
22
has not extended yet, whereby a setting is made to the low lift mode. In the low lift mode, the intake-side cam
26
rotates in the direction of an arrow B. As shown in
FIGS. 27A and 27B
, the cam contact surface
34
a
of the tappet casing
34
comes into contact with the intake-side cam
26
from the base circle section
26
a
through the ramp section
26
c
toward the lift curve section
26
b
. However, since the axially downward displacement of the cam contact portion
34
a
is still small, the tappet casing
34
and the valve stem
35
do not move axially downward yet. As a result of further rotation of the intake-side cam
26
and, as shown in
FIGS. 27C through 27E
, when the cam contact portion
34
a
of the tappet casing
34
proceeds to come into contact with the ramp section
26
c
toward the central portion (nose) of the lift curve section
26
b
, the axially downward displacement of the cam contact portion
34
a
increases. Therefore, the tappet casing
34
and the valve stem
35
are pushed downward against the urging force of a helical (or coiled) spring
36
. As a consequence, the intake valve
18
is also pushed axially downward relative to the valve seat
14
to attain the low lift state. The valve lift amount at this time gradually increases, as shown in
FIG. 27H
, from the stage corresponding to
FIG. 27C
(valve open) and becomes maximum at the stage corresponding to FIG.
27
D. As a result of further rotation of the intake-side cam
26
and, as shown in
FIG. 27E
, once the cam contact portion
34
a
of the tappet casing
34
comes into contact, through the central portion of the lift curve section
26
b
, with the ramp section
26
d
, the axially downward displacement of the cam contact portion
34
a
moves in the direction of decreasing. Therefore, the tappet casing
34
and the valve stem
35
are lifted by the urging force of the helical spring
36
while following the cam profile of the intake-side cam
26
. As a result, the intake valve
18
is also forced against the valve seat
14
, whereby the lifted state is finished (valve closed). The valve lift amoun
Chang Ching
Denion Thomas
Mitsubishi Denki & Kabushiki Kaisha
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