Internal-combustion engines – Poppet valve operating mechanism – Rocker
Reexamination Certificate
1999-06-14
2001-08-14
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Rocker
C123S090450, C123S090470
Reexamination Certificate
active
06273042
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved rocker assembly for use in engines, and to methods of assembling such improved rocker assemblies.
2. Description of the Prior Art
In piston-powered engines for vehicles and tools such as lawnmowers, the engines have a camshaft and crankshaft working in concert. The pistons move up and down in cylinders, driving the crankshaft. The crankshaft is typically linked to the camshaft, so that the camshaft rotates as the crankshaft rotates. As the camshaft rotates, cylinder valves are opened and allowed to close. As one valve opens, air or a fuel-air mixture is allowed to enter the piston cylinder. As another valve opens, exhaust leaves the piston cylinder.
The camshaft has a plurality of spaced cams that rotate as the camshaft rotates. As the cams rotate, they push against push rods, to reciprocate the push rods. Each push rod has one end that bears against one end of a rocker assembly mounted on the engine. The rocker assemblies include rocker arms that are pivotally mounted on the engine. As each the rocker arm pivots, a second end pushes against a bearing surface on a valve stem to open the cylinder valve. A biasing spring returns the valve to the seated position and the rocker arm pivots back to its original position when the camshaft rotates further.
Commonly, the second end of the rocker arm bearing against the valve stem bearing surface has a wear element for pushing against the valve stem bearing surface. Typically, a slight spacing is maintained between the wear element of the rocker arm and the valve stem bearing surface. This desired spacing—referred to as the valve lash distance—typically varies with the engine manufacturer and end use. For example, in a diesel engine, for an air intake valve, the preferred valve lash distance may be 0.012 inch, while for an exhaust valve, the desired valve lash distance may be 0.018 inch, for example. For a lawnmower engine, the desired valve lash distance may be 0.020 inch for both air intake and exhaust valves. The valve lash distance is set by adjusting a set screw on the first end of the rocker arm to thereby raise or lower the second end of the rocker arm toward or away from the top bearing surface on the valve stem.
As the rocker arm operates, the rocker arm pivots the bearing surface through an arc. Thus, the wear surface of the rocker arm pushes against the bearing surface of the valve stem in a scuffing or scraping motion. Accordingly, the rocker arm wear surface contacts the valve stem bearing surface generally along a line. As the rocker arm wear surface wears, the valve lash distance increases beyond the desirable pre-set distance. This increased distance is generally referred to as excessive back lash. As the back lash increases beyond the desired spacing, engine operation can become noisy as there is additional space for the rocker arm to vibrate. In addition, with greater wear, the timing of the opening and closing of the cylinder valves becomes less exact, resulting in less efficient engine operation. Excessive back lash can also contribute to longevity and environmental problems.
One solution to the excessive back lash problem is to reduce wear by providing a ball and socket on the valve end of the rocker arm. An example of a rocker assembly with such a ball and socket design is shown in FIGS.
1
and
3
-
5
. As shown in
FIG. 1
, the rocker assembly
10
includes a rocker arm
12
mounted on a base
14
that is mounted on an engine surface
15
. A first end
16
of the rocker arm has a bearing element
18
juxtaposed with one end
20
of a push rod
22
. The other end
24
of the push rod
22
bears against a cam
26
mounted on a camshaft
28
. The camshaft
28
is rotated by a standard drive mechanism, such as a drive chain (not shown) driven by the engine crankshaft (not shown).
The rocker arm
12
also has a second end
30
. At the second end
30
, a rocker ball
32
is secured to the rocker arm
12
. At least a part of the rocker ball
32
is received in a socket
33
. The rocker arm
12
is pivotable on the base
14
about an axis
34
between the first end
16
and second end
30
of the rocker arm
12
. As the first end
16
of the rocker arm
12
is pushed up by the push rod
22
, the rocker arm is pivoted about the axis
34
to move the second end
30
of the rocker arm
12
and the rocker ball
32
through a path defining an arc.
As shown in
FIGS. 3-5
, the rocker ball
32
has a curved outer surface
36
with a center of curvature
38
and a bottom
40
. The center of curvature
38
is between the bottom
40
of the rocker ball
32
and the second end
30
of the rocker arm
12
. At least part of the rocker ball defines a portion of a sphere. A non-spherical neck or throat
37
extends up from the spherical portion
39
to an insert
41
received in a pocket in the second end
30
of the rocker arm
12
.
As shown in
FIGS. 3-5
, the socket
33
has an exterior bearing surface
42
for bearing against a complementary valve bearing surface
44
for pushing the valve stem
45
. The socket
33
also has an exterior non-bearing surface
46
, an interior surface
48
and an annular top
50
with a central opening
52
to receive the rocker ball
32
. The interior surface
48
of the socket
33
has a bearing surface
54
for contacting a portion of the rocker ball curved outer surface
36
. The interior surface
48
of the socket
33
is curved, although not in a spherical shape. Instead, as in standard ball and socket joints, the interior surface
48
is shaped like a gothic arch, diverging from a low point
56
along a central axis
58
. At the annular top
50
of the socket, the horizontal distance between opposing interior sides
60
,
62
of the interior surface is greater than the diameter of the spherical part
39
of the rocker ball
32
so that the rocker ball may be inserted into the central opening
52
.
To lubricate the interface of the exterior bearing surfaces of the socket and valve element, lubricant channels
70
,
72
are machined in the rocker ball
32
and in the socket
33
. Through these channels
70
,
72
, lubricant is delivered to the interface
74
of the socket exterior bearing surface
42
and the valve bearing surface
44
.
In operation, the rocker ball and socket assembly have an at rest position, illustrated in FIG.
3
. Initially, the rocker ball
32
may be canted slightly to one direction, with the central axis
75
of the rocker ball
32
defining an angle &PHgr; with the central axis
58
of the socket
33
. The central axis
58
of the socket is parallel to and slightly offset from the axis
77
of the valve stem
45
. As the cam
26
pushes up on the push rod
22
, the first end
16
of the rocker arm
12
is raised, pivoting the rocker arm
12
about its axis
34
. As the rocker arm
12
pivots, the second end
30
of the rocker arm is pushed downward, moving the rocker ball
32
through a curved path. As the rocker ball
32
is thus moved, it pivots in the socket
33
. As the rocker arm is pivoted about the axis
34
, the rocker ball
32
and socket
33
pass through an interim position, shown in
FIG. 4
, wherein the central axis
58
of the socket
33
is aligned to be co-linear with the central axis
75
of the rocker ball
32
. At the interim position, the socket bearing surface
42
has slid across the valve bearing surface
44
, as shown. The axes
58
,
75
remain generally parallel with the central axis
77
of the valve stem
45
. As the cam
26
pushes the push rod
22
further upward, the first end
16
of the rocker arm
12
is raised higher, and the second end
30
of the rocker arm
12
is pushed further downward, causing further pivoting of the rocker ball
32
, and linear and sliding movement of the socket
33
. These changes in position are illustrated in
FIG. 5
, wherein the central axis
75
of the rocker ball is pivoted to define an angle &thgr; with the central axis
58
of the socket. The curved outer surface
36
of the rocker ball
32
bears against
Perez Vincent M.
Rempfer David E.
Amsted Industries Incorporated
Brosius Edward J.
Denion Thomas
Nguyen Tu M.
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