Information
-
Patent Grant
-
6792905
-
Patent Number
6,792,905
-
Date Filed
Friday, January 24, 200321 years ago
-
Date Issued
Tuesday, September 21, 200419 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
-
International Classifications
-
Abstract
A compression release mechanism for small internal combustion engines, including a compression release member having an auxiliary cam and a weight section. The compression release member is supported for rotation on an annular bearing surface which is in eccentric relation to the longitudinal axis of the engine camshaft. At engine cranking speeds, the compression release member rotates with the camshaft, and the auxiliary cam projects beyond the base circle of a cam lobe on the camshaft to periodically engage a valve to vent pressure from the engine combustion chamber during the compression stroke of the piston to aid in engine cranking. After the engine starts, rapid rotation of the camshaft causes the compression release member to rotate under the inertial load of the weight section thereof to a position in which the auxiliary cam is retracted within the base circle of the cam lobe such that combustion may proceed in a conventional manner.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to compression release mechanisms for small internal combustion engines of the type used in a variety of applications, such as lawnmowers, generators, pumps, tillers, pressure washers and other lawn and garden implements, or in small utility vehicles such as riding lawnmowers, lawn tractors, and the like.
2. Description of the Related Art
Generally, the intake and exhaust valves of small internal combustion engines may be actuated directly by a camshaft located in the cylinder head, or may be actuated indirectly through the use of rocker arms, tappets, or other similar means. For example, in many existing L-head and overhead valve (“OHV”) engines, the crankshaft drives a camshaft which is located within the crankcase and is disposed parallel to the crankshaft, and lobes on the camshaft actuate lifters, push rods and/or rocker arms to open and close the valves. In overhead cam (“OHC”), engines, a camshaft located in the cylinder head of the engine is driven from the crankshaft, and includes lobes thereon which directly actuate intake and exhaust valves. One such overhead cam engine is disclosed in U.S. Pat. No. 6,295,959, assigned to the assignee of the present invention, the disclosure of which is expressly incorporated herein by reference.
At engine cranking speeds during engine starting, the intake and exhaust valves are both closed as the piston rises toward its top dead center position, and substantial pressure is built up in the combustion chamber which resists movement of the piston toward the top dead center position. This pressure must be overcome to crank the engine for starting, and typically requires a substantial amount of force to be exerted by the operator, such as by pulling on the rope of a recoil starter. Therefore, small internal combustion engines typically include a type of compression release mechanism to aid in engine starting.
Compression release mechanisms for small internal combustion engines are usually operable at cranking speeds to prevent the exhaust valve from fully closing as the piston reaches its top dead center position, thereby allowing venting of pressure from the combustion chamber. In this manner, cranking of the engine is much easier and requires less force to be exerted by the operator. When the engine reaches a predetermined speed after starting, the compression release mechanism is automatically rendered inoperative, such that the exhaust valve fully seats or closes as the piston approaches its top dead center position to allow combustion to proceed in a conventional manner.
A problem with many known compression release mechanisms is that such devices include a large number of individual parts, and are often mechanically complex. Further, such devices typically take up an undesirably large amount of space around the camshaft of the engine.
What is needed is a compression release mechanism for small internal combustion engines which includes a relatively few number of parts, is durable, and which is compact in construction.
SUMMARY OF THE INVENTION
The present invention provides a compression release mechanism for small internal combustion engines, including a compression release member having an auxiliary cam and a weight section. The compression release member is supported for rotation on an annular bearing surface which is in eccentric relation to the longitudinal axis of the engine camshaft. At engine cranking speeds, the compression release member rotates with the camshaft, and the auxiliary cam projects beyond the base circle of a cam lobe on the camshaft to periodically engage a valve to vent pressure from the engine combustion chamber during the compression stroke of the piston to aid in cranking the engine during starting. After the engine starts, rapid rotation of the camshaft causes the compression release member to rotate under the inertial load of the weight section thereof to a position in which the auxiliary cam is retracted within the base circle of the cam lobe such that combustion may proceed in a conventional manner.
More specifically, in one embodiment, the compression release mechanism includes a first collar which is rotationally fixed with respect to the camshaft, the first collar having a hub portion eccentric with respect to the camshaft. A second collar includes an auxiliary cam and a weight section, and is supported for rotation on the hub portion of the first collar between first and second positions. In the first position, which corresponds to engine cranking speeds, a spring connected between the first and second collars biases the second collar to a rotational position in which the auxiliary cam projects beyond the base circle of the cam lobe to engage and at least partially open the valve. In this manner, a portion of the pressure within the combustion chamber is vented during the compression stroke of the piston to aid in engine cranking. After the engine is started and the rotational speed of the camshaft rapidly increases, the inertial load of the weight section of the second collar overcomes the bias force of the spring, and the second collar rotates to a rotational position in which the auxiliary cam is positioned within the base circle of the cam lobe such that the auxiliary cam does not engage the valve, allowing combustion to proceed in a conventional manner.
Advantageously, the construction of the compression release mechanism, which includes the first collar positioned on a crankshaft adjacent the cam lobe, and the second collar supported for rotation upon the first collar, it is very compact in construction, such that the compression release mechanism takes up a minimal amount of space around the camshaft.
The second collar, which includes the auxiliary cam and weight section integrally formed therewith, comprises a single piece supported for rotation upon the first collar. In this manner, the present compression release mechanism includes only one moving part, and is therefore simplified in operation and in construction. Further, forces resulting from the contact between the auxiliary cam and the valve are transferred directly through the second collar and the first collar to the camshaft itself, increasing the operational life and durability of the compression release mechanism.
In one form thereof the present invention provides an internal combustion engine, including a camshaft including a longitudinal axis and at least one cam lobe, the cam lobe including a portion projecting beyond a base circle of the cam lobe for periodically engaging a valve, the camshaft further including an annular bearing surface disposed in eccentric relation with respect to the camshaft longitudinal axis; and a compression release mechanism, including a compression release member including an auxiliary cam, the compression release member supported for rotation on the annular bearing surface between a first position corresponding to engine cranking speeds in which the auxiliary cam is positioned outside of the cam lobe base circle to engage and at least partially open the valve, and a second position corresponding to engine running speeds in which the auxiliary cam is positioned within the cam lobe base circle and does not engage the valve.
In another form thereof, the present invention provides an internal combustion engine, including a camshaft having at least one cam lobe, the cam lobe including a portion projecting beyond a base circle of the cam lobe for periodically engaging a valve; and a compression release mechanism, including a first collar rotationally fixed with respect to the camshaft, the first collar having a hub portion eccentric to the camshaft; a second collar including an auxiliary cam, the second collar supported for rotation on the hub portion of the first collar between a first position corresponding to an engine cranking speed, in which the auxiliary cam is positioned outside of the cam lobe base circle to engage and at least partially open the valve, and a second position corresponding to an engine running speed, in which the auxiliary cam is positioned within the cam lobe base circle and does not engage the valve.
In a further form thereof, the present invention provides an internal combustion engine, including a camshaft having a longitudinal axis and at least one cam lobe, the cam lobe including a portion which projects beyond a base circle of the cam lobe for periodically engaging a valve, the camshaft further including an annular bearing surface having a central axis offset from the longitudinal axis; and a compression release mechanism, including a collar supported for rotation on the bearing surface, the collar including an auxiliary cam, and a weight section disposed around a portion of a circumference of the collar; a spring connecting the camshaft and the collar and biasing the collar to a first position in which the auxiliary cam is positioned outside of the cam lobe base circle to engage and at least partially open the valve, whereby at engine running speeds, the inertia of the weight section overcomes the bias of the spring, causing the collar to rotate to a second position in which the auxiliary cam is positioned within the cam lobe base circle and does not engage the valve.
In a further form thereof, the present invention provides an internal combustion engine, including a camshaft having a longitudinal axis and at least one cam lobe, the cam lobe including a portion projecting beyond a base circle of the cam lobe for periodically engaging a valve; and a compression release mechanism, including an annular bearing surface having a central axis offset from the longitudinal axis of the camshaft; and means, rotatably supported on the bearing surface, for engaging the valve at engine cranking speeds and not engaging the valve at engine running speeds.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
FIG. 1
is an elevational view of an exemplary engine, including a camshaft having a compression release mechanism in accordance with the present invention;
FIG. 2
is a perspective view of the camshaft and the compression release mechanism of the engine of
FIG. 1
;
FIG. 3
is an exploded view of the camshaft and compression release mechanism of
FIG. 2
;
FIG. 4
is a sectional view through the camshaft, taken along line
4
—
4
of
FIG. 2
with the exhaust cam lobe and components of the exhaust valve in phantom, showing the compression release mechanism in a first operational position corresponding to engine cranking speeds;
FIG. 5
is a sectional view through the camshaft, taken along line
5
—
5
of
FIG. 2
with the exhaust cam lobe and components of the exhaust valve in phantom, showing the compression release mechanism in a second operational position corresponding to engine running speeds; and
FIG. 6
is a perspective view of a compression release mechanism according to a second embodiment.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention any manner.
DETAILED DESCRIPTION
Referring to
FIG. 1
, there is shown a single cylinder, 4-stroke internal combustion engine
10
including a compression release mechanism
70
,
120
according to the present invention. Although
FIG. 1
illustrates a single cylinder 4-stroke engine, the present compression release mechanism
70
,
120
is not necessarily limited to this particular type of engine. Additionally, although engine
10
in
FIG. 1
includes a side valve or “L-head” type of valve train configuration as described hereinafter, the compression release mechanism
70
,
120
of the present invention may also be used in overhead valve (“OHV”) engines and in overhead cam (“OHC”) engines. One exemplary overhead cam engine is disclosed in the above-incorporated U.S. Pat. No. 6,295,959.
Engine
10
includes crankcase
12
, cylinder
14
, crankshaft
16
, and piston
18
, with piston
18
being operatively connected to crankshaft
16
through connecting rod
20
. Crankshaft
16
may disposed in either a vertical or a horizontal orientation, depending upon the application in which engine
10
is used. Piston
18
cooperates with cylinder
22
and cylinder head
24
to define a combustion chamber
26
. Spark plug
28
secured in cylinder head
24
ignites a fuel/air mixture therein after the fuel/air mixture has been brought into combustion chamber
26
during the intake stroke and has been compressed during the compression stroke of piston
18
. The spark is normally timed to ignite the fuel/air mixture just before piston
18
completes its assent on the compression stroke. The fuel/air mixture is drawn into combustion chamber
20
from the carburetor of the engine through an intake passage (not shown) having an intake valve therein, and the products of combustion are expelled from combustion chamber
20
during the exhaust stroke through exhaust port
32
controlled by exhaust valve
34
. Exhaust valve
34
additionally functions as a compression release valve in a manner to be discussed hereinafter; however, the intake valve of the engine may also function as a compression release valve using the compression release mechanism
70
,
120
of the present invention.
Engine
10
further includes drive gear
36
mounted on crankshaft
16
for rotation therewith, and camshaft gear
40
mounted on camshaft
38
and rotatably driven by drive gear
36
to thereby rotate camshaft
38
at one-half crankshaft speed. Camshaft
38
includes conventional pear-shaped intake and exhaust camshaft lobes
42
and
44
, respectively, which rotate with camshaft
38
to impart reciprocating motion to the intake valve and to exhaust valve
34
via tappets
50
. In the embodiment shown in the drawings, intake lobe
42
is the inboard lobe adjacent camshaft gear
40
, and exhaust lobe.
44
is outboard of camshaft gear
40
and intake lobe
42
.
Exhaust valve train
48
is shown in
FIG. 1
, and includes tappet
50
which has a circular follower
52
with a flat undersurface adapted to bear tangentially against and track upon the periphery of exhaust lobe
44
. Tappet
50
slides in guide boss
54
of crankcase
12
, and its upper end pushes against the tip of exhaust valve
34
. In operation, tappet
50
lifts the stem of exhaust valve
34
, which lifts face
58
of exhaust valve
34
from valve seat
60
. Valve spring
62
encircles stem
56
between valve guide
54
and spring retainer
64
. Spring
62
biases exhaust valve
34
closed and also biases tappet
50
into tracking contact with exhaust lobe
44
.
To aid in starting engine
10
, mechanical compression release mechanism
70
,
120
is provided according to first and second embodiments which will be described hereinafter. When compression release mechanism
70
,
120
is in an inoperative position, corresponding to engine running speeds, the rotation of exhaust lobe
44
of camshaft
38
causes normal operation of exhaust valve
34
, so that exhaust valve
34
opens and closes in timed and periodic relation with the travel of piston
18
according to conventional timing practice. Thus, exhaust lobe
44
is adapted to open exhaust valve
34
near the end of the power stroke and to hold same open during assent of piston
18
on the exhaust stroke until piston
18
has moved slightly past top dead center. As exhaust lobe
44
continues to rotate, spring
62
forces tappet
50
downwardly and exhaust valve
34
is reseated. Exhaust valve
34
is held in a closed position during the ensuing intake, compression, and power strokes. Intake camshaft lobe
32
is likewise of conventional fixed configuration to control the intake valve such that it completely closes shortly after piston
18
begins its compression stroke and remains closed throughout the subsequent power and exhaust strokes, and reopening to admit the fuel mixture on the intake stroke.
Since in a conventional engine, the intake and exhaust valves are normally closed for the major portion of the compression stroke, cranking of the engine would be difficult unless some provision is made to vent combustion chamber
26
during a part of, or all of, the compression stroke during cranking of engine
10
. However, by incorporating the improved compression release mechanism
70
,
120
of the present invention, compression relief is automatically obtained at cranking speeds to greatly reduce cranking effort and thereby facilitate starting. Moreover, a conventional engine
10
need not be significantly physically altered to effect compression release with the mechanism
70
,
120
of the present invention incorporated therein. The compression release mechanism
70
,
120
is responsive to engine speed such that it is automatically rendered inoperative at engine running speeds so that there is no compression loss to decrease the efficiency of engine
10
when it is running under its own power.
Compression release mechanism
70
according to a first embodiment is shown with reference to
FIGS. 2-5
. Referring first to
FIGS. 2 and 3
, camshaft
38
is shown, which may be made from cast iron or steel, for example. Camshaft
38
includes shaft portion
72
having intake lobe
42
, exhaust lobe
44
, and camshaft gear
40
affixed thereto. Intake and exhaust lobes
42
,
44
, and camshaft gear
40
may be formed of a suitable rigid plastic material which is molded onto shaft portion
72
of camshaft
38
. Intake and exhaust lobes
42
,
44
and camshaft gear
40
may be either integrally formed with one another as a unit which is attached to camshaft
38
, or alternatively, intake and exhaust lobes
42
,
44
and camshaft gear
40
may be formed separately from one another.
Mechanical compression release mechanism
70
is attached to camshaft
38
, and generally includes stop collar
74
, weight collar
76
, and spring
78
. Referring to
FIG. 3
, stop collar
74
may be made from a rigid plastic material, or a suitable metal such as powder metal, aluminum, or steel, for example, and generally includes annular flange
80
and hub annular portion
82
. Hub portion
82
includes bore
84
therethrough, as well as outer annular bearing surface
86
. Bore
84
is disposed along a longitudinal axis which is co-linear with longitudinal axis A
1
—A
1
of shaft portion
72
of camshaft
38
, while annular bearing surface
86
of hub portion
82
has a central axis A
2
—A
2
which is offset from axis A
1
—A
1
. In this manner, annular bearing surface
86
of hub portion
82
is eccentric with respect to bore
84
of hub portion
82
and longitudinal axis A
1
—A
1
of shaft portion
72
of camshaft
38
.
After weight collar
76
, described below, is placed onto hub portion
82
of stop collar
74
, stop collar
74
is inserted onto shaft portion
72
of camshaft
38
, and anchor projection
88
of hub portion
82
is fitted within recess
90
of exhaust cam lobe
44
to fixedly connect stop collar
74
to exhaust cam lobe
44
. Thus, stop collar
74
is rotationally fixed with respect to camshaft
38
, and rotates therewith. Alternatively, stop collar
74
could be fixed with respect to camshaft
38
by welding stop collar
74
directly to shaft portion
72
or to exhaust cam lobe
44
of camshaft
38
, for example. Stop collar
74
additionally includes stop segment
92
integrally formed therewith, which extends in an arcuate manner around at least a portion of the circumference of annular flange
80
of stop collar
74
. Stop segment
92
includes arcuate slot
94
therein, and additionally includes first stop surface
96
and second stop surface
98
at opposite ends thereof.
Although stop collar
74
has been described above as a separate component attached to camshaft
38
, other configurations are possible. For example, hub portion
82
of stop collar
74
may be integrally formed with shaft portion
72
of camshaft
38
, such that camshaft
38
includes annular outer bearing surface
86
for rotationally supporting weight collar
76
. In this configuration, annular flange
80
and stop segment
92
may together comprise a separate component which is fitted onto camshaft
38
in a suitable manner adjacent annular outer bearing surface
86
.
Weight collar
76
is an annular member made from a relatively heavy or dense metal, such as steel or cast iron, for example, and includes inner annular bearing surface
100
rotationally slidable upon outer annular bearing surface
86
of stop collar
74
when weight collar
76
is positioned thereon. Weight collar
76
includes auxiliary cam
102
integrally formed therewith, which extends outwardly from the outer periphery of weight collar
76
. Further, weight collar
76
includes an arcuately-shaped, integral weight section
104
disposed around at least a portion of the circumference thereof. For example, as shown in
FIG. 3
, weight section
104
extends approximately 180° around the circumference of weight collar
76
. Weight section
104
additionally includes hole
106
therein.
Spring
78
connects stop collar
74
and weight collar
76
, and includes first end
110
, second end
112
, and coil portion
114
intermediate first and second ends
110
,
112
. First end
110
of spring
78
is received through arcuate slot
94
of stop collar
74
and slidably engages the rear surface of annular flange
80
of stop collar
74
which is disposed opposite hub portion
82
. Second end
112
of spring
78
is fixedly attached to hole
106
in weight section
104
of weight collar
76
. One suitable spring is 9.5 mm in length from first end
110
to second end
112
when no load is imposed thereon, such as when weight collar
76
is in its first operational position corresponding to engine cranking speeds, as shown in FIG.
4
and described below. This spring stretches to 19.0 mm in length under a load of 14±2 grams in the second operational position of weight collar
76
which corresponds to engine running speeds, as shown in FIG.
5
and described below.
The operation of compression release mechanism
70
will be described with primary reference to
FIGS. 4 and 5
. In
FIG. 4
, compression release mechanism
70
is shown with weight collar
76
disposed in a first rotational position which corresponds to engine cranking speeds. At engine cranking speeds, camshaft
38
rotates relatively slowly in the direction of arrow
108
in
FIG. 4
, and weight collar
76
rotates together with stop collar
74
and camshaft
38
. Further, spring
78
biases weight collar
76
toward the position shown in
FIG. 4
at cranking speeds, in which auxiliary cam
102
of weight collar
76
is disposed proximate the widest or thickest section of hub portion
82
of stop collar
74
, such that auxiliary cam
102
projects beyond the base circle
116
of exhaust cam lobe
44
. In this manner, auxiliary cam
102
will contact follower
52
of tappet
50
during the compression stroke of engine
10
to partially open or unseat exhaust valve
34
in order to release at least a portion of the pressure within combustion chamber
26
as piston
18
approaches top dead center position to aid in engine cranking. Further, first edge
104
a
of weight section
104
of stop collar
74
is disposed proximate first stop surface
96
of stop segment
92
of stop collar
74
.
After engine
10
starts, the rotational speed of camshaft
38
along arrow
108
increases rapidly. However, the inertial load which is inherent from the mass of weight section
104
of weight collar
76
initially resists concurrent rotation of weight collar
76
with stop collar
74
and camshaft
38
. Thus, when the speed of camshaft
38
rapidly increases, the rotational speed of weight collar
76
is initially less than the rotational speed of stop collar
74
and camshaft
38
. The foregoing rotational speed difference between weight collar
76
and stop collar
74
results in rotation of weight collar
76
upon hub portion
82
of stop collar
74
, in which inner annular bearing surface
100
of weight collar
76
rotationally slides with respect to outer annular bearing surface
86
of stop collar
74
.
During an initial extent of rotation of weight collar
76
upon hub portion
82
of stop collar
74
, first end
110
of spring
78
slides within arcuate slot
94
of stop segment
92
until first end
110
of spring
78
contacts the edge of arcuate slot
94
. Due to the need for compression release mechanism
70
to occupy a small spatial area within small engines, the size and thus the mass of weight collar
76
is somewhat limited. Thus, the inertial force of weight collar
76
is correspondingly limited. In this manner, for many applications in which compression release mechanism
70
is used, a type of spring having a load which increases proportionally with increasing spring length as the spring is stretched may not be desirable because, as weight collar
76
rotates and the spring stretches, the spring load could eventually overcome the inertial force of weight collar
76
to thereby inhibit rotation of weight collar
76
upon hub portion of stop collar
74
. However, in compression release mechanism
70
, first end
110
of spring
78
slides within arcuate slot
94
of stop segment
92
during an initial portion of the rotation of weight collar
76
, such that spring
78
does not begin to stretch and to thereby impose a load until a later point in the rotational progression of weight collar
76
. In this manner, as described below, the load of the stretched spring
78
will not overcome the inertial load of weight collar
76
at engine running speeds.
As an alternative to the configuration of stop collar
74
, weight collar
76
, and spring
78
shown in
FIGS. 2-6
and described herein, arcuate slot
94
may be removed, and a spring having a spring load which remains constant throughout the stretching of the spring may be connected directly between stop collar
74
and weight collar
76
, wherein the constant load of such a spring is selected such that it does not overcome the inertial load of weight collar
76
at engine running speeds.
Referring again to
FIGS. 4 and 5
, after first end
110
of spring
78
contacts the edge of arcuate slot
94
, the inertial load of weight section
104
of weight collar
76
overcomes the spring load of spring
78
as the rotational speed of camshaft
38
increases, and continued rotation of weight collar
76
upon hub portion
82
of stop collar
74
forces coil portion
114
of spring
78
to expand, thereby stretching spring
78
under tension. Weight collar
76
rotates upon hub portion
82
of stop collar
74
until second edge
104
b
of weight section
104
contacts second stop surface
98
of stop segment
92
of stop collar
74
, as shown in
FIG. 5
, and the engagement between weight section
104
and stop segment
92
of stop collar
74
forces weight collar
76
to rotate together with stop collar
74
and camshaft
38
. Weight collar
76
remains in this position, shown in
FIG. 5
, at engine running speeds with spring
78
stretched under tension. Weight collar
76
rotates approximately 90° between its first operational position shown in FIG.
4
and its second operational position shown in FIG.
5
.
Referring to
FIGS. 4 and 5
, during rotation of weight collar
76
upon hub portion
82
of stop collar
74
, auxiliary cam
102
of weight collar
76
rides around the outer annular bearing surface of hub portion
82
, which is eccentric to shaft portion
72
of camshaft
38
. In particular, auxiliary cam
102
moves from a first position shown in
FIG. 4
in which auxiliary cam
102
is disposed proximate the widest or thickest section of hub portion
82
, to a second position shown in
FIG. 5
in which auxiliary cam
102
is disposed proximate a more narrow or thin section of hub portion
82
. In this manner, as auxiliary cam
102
rotates with weight collar
76
around the eccentric hub portion
82
of stop collar
74
, auxiliary cam
102
is progressively retracted within base circle
116
of exhaust cam lobe
44
. In the position of
FIG. 5
corresponding to engine running speeds, auxiliary cam
102
is disposed completely within base circle
116
of exhaust cam lobe
44
, such that auxiliary cam
102
no longer contacts follower
52
of tappet
50
, such that exhaust valve
34
may fully close or seat as piston
18
approaches its top dead center position to allow combustion within engine
10
to proceed in a conventional manner.
Upon shutdown of engine
10
, the rotational speed of camshaft
38
decreases rapidly. However, the rotational speed of weight collar
76
decreases less rapidly due to the inertial load of weight section
104
of weight collar
76
, which urges weight collar
76
to continue to rotate at engine running speed. The difference in the decrease of rotational speed between stop collar
74
(and camshaft
38
) and weight collar
76
causes “over-rotation” of weight collar
76
, wherein weight collar
76
rotates upon hub portion
82
of stop collar
74
from the position shown in
FIG. 5
back to the position shown in FIG.
4
. Also, the decrease in rotational speed of weight collar
76
reduces the inertial load of weight section
104
, such that a return force exerted by the contraction of coil portion
114
of spring
78
overcomes the inertial load of weight section
104
and allows spring
78
to bias weight collar
76
back to the position shown in FIG.
4
.
Advantageously, when compression release mechanism
70
is disposed in the position shown in
FIG. 4
at engine cranking speeds, contact forces between follower
52
of tappet
50
and auxiliary cam
102
are transmitted directly through weight collar
76
and stop collar
74
to camshaft
38
itself, and therefore are not distributed to other parts of the compression release mechanism
70
, such as weight section
104
and spring
78
. In addition, compression release mechanism
70
includes only one moving part, namely, weight collar
76
. For the foregoing reasons, compression release mechanism
70
is less prone to fatigue or failure, increasing the operational life of compression release mechanism
70
.
Further, referring to
FIG. 2
, it can be seen that weight collar
76
, which is rotationally supported upon hub portion
82
of stop collar
74
, has a relatively thin profile and is disposed directly adjacent exhaust cam lobe
44
, such that the width of compression release mechanism
70
between exhaust cam lobe
44
and annular flange
80
of stop collar
74
is minimized, and space within engine
10
is conserved.
Referring to
FIG. 6
, compression release mechanism
120
according to a second embodiment is shown, including stop collar
74
and weight collar
76
, which are each substantially similar to those described above with respect to compression release mechanism
70
. In the embodiment of
FIG. 6
however, spring
122
includes coil portion
123
, first end
124
defining slot portion
128
therein, and second end
126
connected to weight section
102
of weight collar
76
. Pin
130
is received through slot portion
128
of spring
122
, and is fitted within an aperture
132
in stop collar
74
.
The operation of compression release mechanism
120
is identical to that of compression release mechanism
70
according to the first embodiment as described above, except that, during initial rotation of weight collar
76
upon hub portion
82
of stop collar
74
after engine
10
is started and the speed of rotation of camshaft
38
rapidly increases, slot portion
128
of spring
122
guidingly slides around pin
130
until pin
130
contacts the end of slot portion
128
. Thereafter, further rotation of weight collar
76
causes spring
122
to be placed under tension. Upon engine shutdown, spring
122
returns weight collar
76
to its initial position, shown in FIG.
6
.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
Claims
- 1. An internal combustion engine, comprising:a camshaft including a longitudinal axis and at least one cam lobe, said cam lobe including a portion projecting beyond a base circle of said cam lobe for periodically engaging a valve, said camshaft further including an outer annular bearing surface disposed in eccentric relation with respect to said camshaft longitudinal axis, and a compression release mechanism, comprising: a compression release member including an auxiliary cam and an inner annular bearing surface rotatably supported on said outer annular bearing surface between a first position corresponding to engine cranking speeds in which said auxiliary cam is positioned outside of said cam lobe base circle to engage and at least partially open said valve, and a second position corresponding to engine running speeds in which said auxiliary cam is positioned within said cam lobe base circle and does not engage said valve.
- 2. The internal combustion engine of claim 1, further comprising a spring connected between said camshaft and said compression release member, said spring biasing said compression release member to said first position.
- 3. An internal combustion engine, comprising:a camshaft including a longitudinal axis and at least one cam lobe, said cam lobe including a portion projecting beyond a base circle of said cam lobe for periodically engaging a valve, said camshaft further including an annular bearing surface disposed in eccentric relation with respect to said camshaft longitudinal axis; and a compression release mechanism, comprising: an annular compression release member including an auxiliary cam and a weight section disposed around a portion of a circumference thereof, said compression release member supported for rotation on said annular bearing surface between a first position corresponding to engine cranking speeds in which said auxiliary cam is positioned outside of said cam lobe base circle to engage and at least partially open said valve, and a second position corresponding to engine running speeds in which said auxiliary cam is positioned within said cam lobe base circle and does not engage said valve.
- 4. The internal combustion engine of claim 3, further comprising a pair of stop surfaces cooperating with said annular bearing surface, said stop surfaces engageable with said weight section of said compression release member to define rotational limits of said compression release member between said first and second positions.
- 5. The internal combustion engine of claim 4, wherein said annular bearing surface and said stop surfaces are formed together as a collar member, said collar member fixed for rotation with said camshaft.
- 6. An internal combustion engine, comprising:a camshaft having at least one cam lobe, said cam lobe including a portion projecting beyond a base circle of said cam lobe for periodically engaging a valve; and a compression release mechanism, comprising: a first collar rotationally fixed with respect to said camshaft, said first collar having a hub portion eccentric to said camshaft; a second collar including an auxiliary cam, said second collar supported for rotation on said hub portion of said first collar between a first position corresponding to an engine cranking speed, in which said auxiliary cam is positioned outside of said cam lobe base circle to engage and at least partially open said valve, and a second position corresponding to an engine running speed, in which said auxiliary cam is positioned within said cam lobe base circle and does not engage said valve.
- 7. The internal combustion engine of claim 6, wherein said camshaft includes a longitudinal axis, and said hub portion of said first collar includes a central axis which is offset from said longitudinal axis.
- 8. The internal combustion engine of claim 6, wherein said hub portion of said first collar defines an outer annular bearing surface, and said second collar defines an inner annular bearing surface rotatably supported on said outer annular bearing surface.
- 9. The internal combustion engine of claim 6, wherein said first collar and said cam lobe are fixedly connected to one another.
- 10. The internal combustion engine of claim 6, wherein said second collar is annular in shape, and includes a weight section disposed around a portion of a circumference of said second collar.
- 11. The internal combustion engine of claim 10, wherein said first collar includes a pair of stop surfaces engageable with said weight section of said second collar to define rotational limits of said second collar between said first and second positions.
- 12. The internal combustion engine of claim 6, further comprising a spring connected between said first collar and said second collar, said spring biasing said second collar to said first position.
- 13. An internal combustion engine, comprising:a camshaft having a longitudinal axis and at least one cam lobe, said cam lobe including a portion which projects beyond a base circle of said cam lobe for periodically engaging a valve, said camshaft further including an annular bearing surface having a central axis offset from said longitudinal axis; and a compression release mechanism, comprising: a collar supported for rotation on said bearing surface, said collar including an auxiliary cam, and a weight section disposed around a portion of a circumference of said collar; a spring connecting said camshaft and said collar and biasing said collar to a first position in which said auxiliary cam is positioned outside of said cam lobe base circle to engage and at least partially open said valve, whereby at engine running speeds, the inertia of said weight section overcomes the bias of said spring, causing said collar to rotate to a second position in which said auxiliary cam is positioned within said cam lobe base circle and does not engage said valve.
- 14. The internal combustion engine of claim 13, wherein said collar includes a pair of radially spaced stop surfaces cooperating with said annular bearing surface thereof.
- 15. The internal combustion engine of claim 14, wherein in said first position, said weight section of said collar is disposed adjacent one of said stop surfaces, and in said second position, said weight section engages the other of said stop surfaces.
- 16. The internal combustion engine of claim 13, wherein said annular bearing surface and said stop surfaces are formed together as a collar member, said collar member fixed for rotation with said camshaft.
- 17. An internal combustion engine, comprising:a camshaft having a longitudinal axis and at least one cam lobe, said cam lobe including a portion projecting beyond a base circle of said cam lobe for periodically engaging a valve; and a compression release mechanism, comprising: an annular outer bearing surface having a central axis offset from said longitudinal axis of said camshaft; and means, rotatably supported on said bearing surface, for engaging said valve at engine cranking speeds and not engaging said valve at engine running speeds.
- 18. The internal combustion engine of claim 17, wherein said engaging means comprises a weight section, said weight section inertially positioning said engaging means responsive to engine speed.
- 19. The internal combustion engine of claim 17, further comprising means for positioning said engaging means at engine cranking speeds such that said engaging means engages said valve.
US Referenced Citations (6)
Foreign Referenced Citations (1)
Number |
Date |
Country |
42 21 394 |
Jan 1994 |
DE |