U.S. patent application number 12/285084 was filed with the patent office on 2010-04-01 for compression release mechanism.
This patent application is currently assigned to S & S Cycle, Inc.. Invention is credited to Jeffrey Bailey, James Havlik, Kyle Mahan, Roy Meyer, Randy Williams.
Application Number | 20100077980 12/285084 |
Document ID | / |
Family ID | 42056042 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100077980 |
Kind Code |
A1 |
Havlik; James ; et
al. |
April 1, 2010 |
COMPRESSION RELEASE MECHANISM
Abstract
A compression release assembly is disclosed, the assembly
including a camshaft rotatable about a camshaft axis, a trigger
rotatable about a trigger axis substantially perpendicular to the
camshaft axis, and a spring position between the trigger and the
camshaft. Preferably, the trigger is rotated from an engagement
position toward a disengagement position when a rotational velocity
of the camshaft achieves a known value, and is rotated from the
disengagement position toward the engagement position when the
rotational velocity of the camshaft is below the known value.
Inventors: |
Havlik; James; (Viola,
WI) ; Mahan; Kyle; (Palmyra, WI) ; Williams;
Randy; (Viola, WI) ; Bailey; Jeffrey; (Westby,
WI) ; Meyer; Roy; (Richland Center, WI) |
Correspondence
Address: |
PRICE HENEVELD COOPER DEWITT & LITTON, LLP
695 KENMOOR, S.E., P O BOX 2567
GRAND RAPIDS
MI
49501
US
|
Assignee: |
S & S Cycle, Inc.
Viola
WI
|
Family ID: |
42056042 |
Appl. No.: |
12/285084 |
Filed: |
September 29, 2008 |
Current U.S.
Class: |
123/182.1 ;
123/90.6; 74/568R |
Current CPC
Class: |
Y10T 74/2102 20150115;
F01L 13/085 20130101; F01L 1/14 20130101 |
Class at
Publication: |
123/182.1 ;
74/568.R; 123/90.6 |
International
Class: |
F01L 13/08 20060101
F01L013/08 |
Claims
1. A compression release assembly comprising: a camshaft rotatable
about a camshaft axis and including a camshaft lobe; a trigger
rotatably mounted on the camshaft about a trigger axis, the trigger
axis being substantially perpendicular to the camshaft axis and
intersecting the trigger between first and second distal ends of
the trigger, the trigger including a compression release lobe
formed at the first distal end of the trigger proximate to the
camshaft lobe; and a counterweight formed at the second distal end
of the trigger, the tripper being L shaped and positioning the
first and second distal ends on a same side of the camshaft axis;
and a spring positioned between the camshaft and the trigger, the
spring tending to rotate the trigger about the trigger axis toward
an engagement position, wherein when the camshaft is rotating at or
above a sufficient velocity, centripetal forces acting on the
counterweight overcome spring biasing such that the trigger rotates
from the engagement position to a disengagement position.
2. The assembly of claim 1, wherein the sufficient velocity is in a
range of about 625 revolutions per minute and about 725 revolutions
per minute.
3. The assembly of claim 2, wherein the sufficient velocity is
about 700 revolutions per minute.
4. The assembly of claim 1, further comprising: a pin extending
along the trigger axis, the pin rotatably coupling the trigger to
the camshaft.
5. The assembly of claim 1, wherein the spring has a spring axis
substantially perpendicular to the camshaft axis.
6. The assembly of claim 5, wherein the spring axis is
substantially perpendicular to the trigger axis.
7. The assembly of claim 1, wherein the spring has a spring axis
substantially parallel to the camshaft axis.
8. The assembly of claim 7, wherein the spring axis is
substantially perpendicular to the trigger axis.
9. The assembly of claim 1, wherein the spring comprises a
compression spring.
10. The assembly of claim 1, wherein the trigger is oriented
relative to the camshaft such that the compression release lobe is
positioned in a lifter roller path of travel when the trigger is in
the engagement position.
11. The assembly of claim 10, wherein the compression release lobe
comprises a lifter roller engagement surface arced between a first
end and a second end, both the first end and the second end being
at a same distance from the trigger axis.
12. The assembly of claim 11, wherein the trigger is oriented
relative to the camshaft such that the lifter roller engagement
surface arcs about the camshaft axis when the trigger is in the
engagement position.
13. The assembly of claim 11, wherein the compression release lobe
includes beveled edges extending along at least a portion of the
lifter roller engagement surface.
14. The assembly of claim 11, wherein the camshaft lobe includes a
recess, and wherein the recess receives the compression release
lobe when the trigger is in the engagement position, and wherein
the recess is of sufficient volume to permit direct contact between
the lifter roller engagement surface and a lifter roller.
15. The assembly of claim 1, wherein the trigger includes a through
hole proximate to the counterweight.
16. An apparatus comprising: an engine including a camshaft
rotatable about a camshaft axis and including a camshaft lobe; and
a compression release assembly including a tripper rotatably
mounted on the camshaft about a trigger axis, the tripper axis
being substantially perpendicular to the camshaft axis and
intersecting the tripper between first and second distal ends of
the trigger, the tripper including a compression release lobe
formed at the first distal end of the trigger proximate to the
camshaft lobe; and a counterweight formed at the second distal end
of the trigger, the trigger being L shaped and positioning the
first and second distal ends on a same side of the camshaft axis;
and a spring positioned between the camshaft and the tripper, the
spring tending to rotate the trigger about the trigger axis toward
an engagement position, wherein when the camshaft is rotating at or
above a sufficient velocity, centripetal forces acting on the
counterweight overcome spring biasing such that the trigger rotates
from the engagement position to a disengagement position.
17. The apparatus of claim 16. including a vehicle frame with the
engine mounted thereon.
18. The apparatus of claim 17, including two wheels on the vehicle
frame to thus form a motorcycle.
19. A method of selectably releasing compression in an engine,
comprising: providing a camshaft defining a camshaft axis;
releasably holding a trigger in an engagement position with a
spring, the trigger including a compression release lobe formed at
a first distal end of the trigger and a counterweight formed at a
second distal end of the trigger and a trigger axis defining with
the first and second distal ends an L shaped arrangement so that
the first and second ends are on a same side of the camshaft axis
when assembled to the camshaft; contacting a compression release
lobe of the trigger with a lifter when the trigger is in the
engagement position; rotating, about the camshaft axis, the trigger
at a rotational velocity; rotating, about the trigger axis
perpendicular to the camshaft axis, the trigger from the engagement
position toward a disengagement position when the rotational
velocity achieves a known value; contacting a camshaft lobe with
the lifter when the trigger is in the disengagement position; and
rotating, about the trigger axis, the trigger from the
disengagement position toward the engagement position when the
rotational velocity is below the known value.
20. A compression release assembly comprising: means for selectably
contacting a compression release lobe of a trigger with a lifter;
means for rotating, about a trigger axis perpendicular to a
camshaft axis, the trigger from an engagement position toward a
disengagement position when a rotational velocity of a camshaft
achieves a known value, the tripper being L shaped and including
first and second distal ends on a same side of the camshaft axis;
and means for rotating, about the trigger axis, the trigger from
the disengagement position toward the engagement position when the
rotational velocity of the camshaft is below the known value.
21. A compression release assembly comprising: a camshaft rotatable
about a camshaft axis and including a camshaft lobe and opposing
outwardly-facing flat engagement surfaces; a ring defining an
opening with inward-facing mating engagement surfaces slidably
engaging the flat engagement surfaces for mounting the ring on the
camshaft and including a counterweight formed at a first distal end
of the ring; and a compression release lobe formed at a second
distal end of the ring; and a spring positioned between the
camshaft and the ring, the spring tending to slide the ring
relative to the camshaft into an engagement position, wherein when
the camshaft is rotating at or above a sufficient velocity,
centripetal forces acting on the counterweight overcome spring
biasing such that the ring slides from the engagement position to a
disengagement position.
22. The assembly of claim 21, wherein the ring further includes an
engagement surface, and wherein contact between a lifter assembly
and the compression release lobe while in the engagement position
causes the engagement surface to engage a corresponding surface on
the camshaft so as to lock the ring in place relative to the
camshaft.
23. A compression release assembly comprising: a camshaft rotatable
about a camshaft axis and including a camshaft lobe and a
trigger-receiving recess not extending through the camshaft; a
trigger rotatably mounted on the camshaft about a trigger axis, the
trigger axis being substantially perpendicular to the camshaft axis
and intersecting the trigger between first and second distal ends
of the trigger, the trigger including a compression release lobe
formed at the first distal end of the trigger proximate to the
camshaft lobe; and a counterweight formed at the second distal end
of the trigger; and a spring positioned between the camshaft and
the trigger, the spring tending to rotate the trigger about the
trigger axis toward an engagement position, wherein when the
camshaft is rotating at or above a sufficient velocity, centripetal
forces acting on the counterweight overcome spring biasing such
that the trigger rotates from the engagement position to a
disengagement position.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to compression release
mechanisms and more particularly to compression release mechanisms
preferably used in motorcycle engines.
DESCRIPTION OF THE RELATED ART
[0002] Compression release mechanisms have been used to reduce
undesirable forces associated with the operation of an engine, such
as forces resisting the starting of an internal combustion engine.
Exemplary compression release mechanisms are described, for
example, in U.S. Pat. Nos. 4,790,271; 4,615,312; and 4,453,507,
which are incorporated by reference herein in their entirety. Known
compression release mechanisms, however, suffer from various
problems.
[0003] In one exemplary design, a loosely fitting ring is utilized
with a decompression lobe mounted on the camshaft. The ring is held
from rotating by two pins and a spring mounted on the camshaft. At
starting speeds, the ring will partially rotate until it is lifted
onto one of the pins on the camshaft. At this point, the cam
follower will ride up the decompression lobe, causing a valve to
open and partially relieve cranking compression. After startup the
ring gets pulled out by rotational forces for normal engine
operation.
[0004] One problem with the above referenced design relates to the
loose fit of the ring. In particular, because the ring fits loosely
on the camshaft, the ring tends to be very unsteady at low and
rough idling speeds of some internal combustion engines. The
unsteadiness, in turn, can cause erratic engagement in a running
internal combustion engine. One of skill in the art would
appreciate the undesirableness of such erratic engagement.
[0005] Another problem with the above referenced design relates to
the robustness of the assembly. In particular, the design relies on
the use of small pins to hold it in place during the decompression
mode. One of skill in the art would appreciate that, at least with
respect to internal combustion engines with high valve spring
forces, the use of small pins would not be robust enough to handle
the high spring force.
[0006] A need thus exists for an improved compression release
mechanism that addresses one or more of the above referenced
problems, or other problems relating to known compression release
mechanisms.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is an exploded assembly view of a compression release
mechanism according to an embodiment of the present invention.
[0008] FIG. 2 is a side view of the compression release mechanism
of FIG. 1 according to an embodiment of the present invention.
[0009] FIG. 3 is a side view of the compression release mechanism
of FIG. 1 according to another embodiment of the present
invention.
[0010] FIG. 4 is a side view of the compression release mechanism
of FIG. 1 according to another embodiment of the present
invention.
[0011] FIG. 5 is a side view of the compression release mechanism
of FIG. 1 according to another embodiment of the present
invention.
[0012] FIG. 6 is a side view of a camshaft with the compression
release mechanism of FIG. 1 in a disengagement position according
to an embodiment of the present invention.
[0013] FIG. 7 is a side view of the camshaft and compression
release mechanism of FIG. 6 with the compression release mechanism
in an engagement position according to an embodiment of the present
invention.
[0014] FIG. 8 is an exploded assembly view of a compression release
mechanism usable with a front exhaust camshaft according to another
embodiment of the present invention.
[0015] FIG. 9 is an exploded assembly view of a compression release
mechanism usable with a rear exhaust camshaft according to another
embodiment of the present invention.
[0016] FIG. 10 is a cross sectional view of a rear exhaust camshaft
and a front exhaust camshaft with associated lifter assemblies and
associated triggers according to an embodiment of the present
invention.
[0017] FIG. 11 is a cross sectional view of a camshaft with a
trigger in an engagement position as may be used with a front
exhaust camshaft according to an embodiment of the present
invention.
[0018] FIG. 12 is a cross sectional view of the camshaft of FIG. 11
with the trigger of FIG. 11 in a disengagement position according
to an embodiment of the present invention.
[0019] FIG. 13 is a cross sectional view of a camshaft with a
trigger in an engagement position as may be used with a rear
exhaust camshaft according to an embodiment of the present
invention.
[0020] FIG. 14 is a cross sectional view of the camshaft of FIG. 13
with the trigger of FIG. 13 in a disengagement position according
to an embodiment of the present invention.
[0021] FIG. 15 is a cross sectional view of the camshaft of FIG. 13
from the opposite side, including a cross sectional view of the
trigger shown in FIG. 13.
[0022] FIG. 16 is a cross sectional view of the camshaft of FIG. 13
from the opposite side.
[0023] FIG. 17 depicts the cross sectional view of FIG. 15 rotated
partially about a spring axis.
[0024] FIG. 18 depicts the cross sectional view of FIG. 16 rotated
partially about a spring axis.
[0025] FIG. 19 depicts the cross sectional view of FIG. 16 rotated
partially about a spring axis.
[0026] FIG. 20 depicts the cross sectional view of FIG. 16 rotated
partially about a spring axis.
[0027] FIG. 21 depicts the cross sectional view of FIG. 16 rotated
partially about a spring axis and partially about a camshaft
axis.
[0028] FIG. 22 depicts a perspective view of a camshaft, a
compression release mechanism, and a lifter assembly according to
an embodiment of the present invention.
[0029] FIG. 23 depicts the camshaft, compression release mechanism,
and lifter assembly of FIG. 22 rotated partially about a spring
axis and partially about a camshaft axis.
[0030] FIG. 24 depicts a cross sectional view of a camshaft with a
trigger in an engagement position as may be used with a rear
exhaust camshaft according to an embodiment of the present
invention.
[0031] FIG. 25 is a perspective view of the trigger shown in FIG.
24.
[0032] FIG. 26 is another perspective view of the trigger shown in
FIG. 24.
[0033] FIG. 27 is a front end view of the trigger shown in FIG.
24.
[0034] FIG. 28 is a top view of the trigger shown in FIG. 24.
[0035] FIG. 29 is a top view of the trigger shown in FIG. 24.
[0036] FIG. 30 is a close up view of contact between the trigger
shown in FIG. 24 and a lifter assembly, and depicts an optional cut
out/recessed portion of a camshaft lobe proximate to a compression
release lobe.
[0037] FIG. 31 is a cross sectional view of a compression release
mechanism according to another embodiment of the present
invention.
[0038] FIG. 32 is a perspective view of the compression release
mechanism of FIG. 31, with the trigger in a disengagement position
according to an embodiment of the present invention.
[0039] FIG. 33 is a side view of the trigger of the embodiment
shown in FIG. 31.
[0040] FIG. 34 is a perspective view of the trigger shown in FIG.
33.
[0041] FIG. 35 is a side by side comparison of the trigger from the
embodiment of FIG. 33 with the trigger from the embodiment of FIG.
24.
[0042] FIGS. 36 and 37 show the camshaft form the embodiment of
FIG. 33, with FIG. 37 being a cross section of FIG. 36 along line
A-A.
[0043] FIGS. 38 and 39 show the camshaft from the embodiment of
FIG. 24, with FIG. 39 being the cross section of FIG. 38 along line
F-F.
[0044] FIG. 40 depicts a side view of a compression release
mechanism with a trigger in an engagement position according to an
embodiment of the present invention.
[0045] FIG. 41 depicts a side view of the compression release
mechanism of FIG. 40 with the trigger in a disengagement position
according to an embodiment of the present invention.
[0046] FIG. 42 is a perspective view of the embodiment shown in
FIG. 40.
[0047] FIG. 43 is a flowchart of a method of selectably releasing
compression in an engine according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0048] As illustrated in the discussion below, various embodiments
of the present invention are directed at a compression release
mechanism for use in an internal combustion engine such as a V-twin
motorcycle engine. Examples include original equipment manufacturer
(OEM) applications and retrofit applications, such as use with Twin
Cam.RTM. and Sportster.RTM. style engines. One exemplary motorcycle
engine is described in WO 2006/083350 (Aug. 10, 2006), which is
incorporated by reference herein in its entirety. It should be
appreciated, however, that one or more of these embodiments may
also be used in other applications, such as automotive engines, all
terrain vehicle (ATV) engines, personal watercraft and boat
engines, snowmobile engines, commercial equipment engines, lawn and
garden equipment engines, etc. Thus, the disclosed embodiments
should not be construed as being limited solely to motorcycle
engine applications. Moreover, one of skill in the art would
appreciate that various materials and manufacturing processes can
be used for one or more components of the disclosed embodiments.
Exemplary materials include billet aluminum and steel (e.g.,
stainless steel).
[0049] Turning now to the embodiments of FIGS. 1-7, the compression
release mechanisms shown include a ring 110 detachably positioned
on a camshaft 210. The ring 110 includes a counterweight 125, an
engagement surface 120, and a compression release lobe 115. The
camshaft 210 preferably includes a flat 215 on which the ring 110
is slidably engaged, an engagement surface 220 which engages
engagement surface 120 of ring 110, and a pocket 225 which receives
a spring 340. In some applications, a removable retaining collar
300 may be provided with or without a set screw for easy
assembly/disassembly.
[0050] In at least one mode of operation, the ring 110 is
positioned on a camshaft 210 such that the ring 110 is held from
rotating (relative to the camshaft 210) by preferably two flats 215
(though one flat, or more than two flats could be used) on the
camshaft 210. For discussion purposes, two positions will be
discussed in detail below: (i) an "engagement position" in which a
compression release lobe 115 is positioned so as to engage a valve
assembly (e.g., by way of direct contact with a lifter assembly);
and (ii) a "disengagement position" in which a compression release
lobe 115 is positioned so as to avoid engagement with the valve
assembly. The engagement position is shown, for example, in FIG. 7.
The disengagement position is shown, for example, in FIG. 6. The
ring 110 of the present embodiment is selectively slid (relative to
the camshaft 210) between the engagement position and the
disengagement position as discussed in greater detail below.
[0051] Selective sliding of the ring 110 can be achieved by way of
interplay between centripetal forces operating on counterweight 125
(when rotating) and spring forces operating on spring engagement
surfaces of ring 110/camshaft 210 (at all times). In particular, at
all RPMs the spring 340 provides a relative force between the ring
110 and the camshaft 210 tending to cause sliding of the ring 110
into the engaged position and to hold the ring 110 therein.
However, as the rotational velocity of the camshaft 210 gradually
increases, the centripetal forces acting on counterweight 125
similarly gradually increase. These centripetal forces tend to
cause a sliding of ring 110 opposite the sliding caused by spring
340. At some known rotational velocity (and at rotational
velocities above this known value) that depends on spring 340
parameters and ring 110 parameters, the force on ring 110 caused by
centripetal forces acting on counterweight 125 exceeds the force
caused by spring 340. Thus, the ring 110 slides from the engagement
position toward the disengagement position. When the rotational
velocity falls below the known value (e.g., when the engine is
turned off), the force caused by spring 340 again exceeds the
forces caused by centripetal forces acting on counterweight 125,
and the ring 110 slides back toward the engagement position from
the disengagement position. In this manner, the ring 110 is
selectively slid between the engagement position and the
disengagement position.
[0052] The operation of ring 110 relative to camshaft 210 can also
be observed by reference to FIGS. 3-5. As the lifter follows the
base circle, it catches a lobe 115 protruding from the ring 110.
This slides the ring 110 along the flat 215 on the cam lobe. As the
camshaft 210 continues to rotate, the lifter rides along the lobe
115 and pushes the spring loaded ring 110 down such that an
engagement surface 120 of the ring 110 engages a corresponding
engagement surface 220 of camshaft 210. See, for example, contact
point 310 in FIG. 5 where the lifter assembly contacts the lobe
115. Now locked in place, the lobe 115 forces the lifter up
slightly at the lobe 115, causing the exhaust valve to crack open
during the compression stroke, relieving a certain amount of
cylinder pressure. The exhaust valve then returns closed, allowing
the engine to start with much less cranking compression. When the
engine starts, increased rotational speed generates enough
rotational force to cause a counterweight 125 on the ring 110 to
act against a spring 340 in a pocket 225 of camshaft 210 and stay
in the disengaged position for normal engine operation.
[0053] Turning next to the embodiments of FIGS. 8-30, the
compression release mechanisms shown include a camshaft 1060
rotatable about a camshaft axis 1065, a trigger 1000 rotatable
about a trigger axis 1015 that is substantially perpendicular to
camshaft axis 1065, and a spring 1040 positioned between the
camshaft 1060 and the trigger 1000 (the spring preferably being
aligned along a spring axis 1045 shown best in FIGS. 11 and 12). In
the embodiment shown in FIGS. 11 and 12, the axes 1015 and 1065
intersect. However, axes 1015 and 1065 may be offset in some
applications. Preferably, the camshaft 1060 includes a camshaft
lobe 1070 with an obround shape relative to the camshaft axis 1065,
and a first spring engagement surface for engaging spring 1040. The
trigger 1000 preferably includes a compression release lobe 1030
formed at a first distal end of the trigger 1000 proximate to the
camshaft lobe 1070, a counterweight 1020 formed at a second distal
end of the trigger 1000, and a second spring engagement surface for
engaging spring 1040. The trigger 1000 may be rotatably coupled to
the camshaft 1060 by a pin 1010 and associated nut 1050 or by other
suitable fastener techniques.
[0054] As shown for example in FIG. 10, the compression release
mechanism can be used in a variety of applications. Shown on the
left of FIG. 10 is a trigger 1000 positioned with an associated a
rear exhaust camshaft 1061 (a cross section thereof is depicted)
that actuates a lifter assembly 1080 for the rear exhaust valve of
a twin cylinder motorcycle engine. Shown on the right of FIG. 10 is
a trigger 1000 positioned with an associated front exhaust camshaft
1062 (a cross section thereof is depicted) that actuates a lifter
assembly 1090 for the front exhaust valve of the twin cylinder
motorcycle engine. The camshafts 1061, 1062 shown rotate in a
clockwise direction about associated camshaft axes. The triggers
1000 rotate about trigger axes 1015 substantially perpendicular to
the associated camshaft axes 1065, and as part of the complete
compression release mechanisms that rotate about the camshaft axes
1065 in response to rotation of the associated camshafts 1061,
1062.
[0055] In at least one mode of operation, the compression release
mechanism described above is configured to selectively contact a
lifter assembly 1080, 1090 with a compression release lobe 1030 of
trigger 1000. Namely, the compression release lobe 1030 of a given
trigger 1000 is selectively rotated into and out of a lifter roller
path of travel so as to selectively contact an associated lifter
assembly 1080, 1090. For discussion purposes, two positions will be
discussed in detail below: (i) an "engagement position" in which a
compression release lobe 1030 is positioned so as to engage a valve
assembly (e.g., by way of direct contact with a lifter assembly
1080, 1090); and (ii) a "disengagement position" in which a
compression release lobe 1030 is positioned so as to avoid
engagement with the valve assembly. FIGS. 11 and 13 show an
exemplary trigger 1000 and camshaft 1060 with a trigger 1000
oriented in an engagement position. FIGS. 12 and 14 show the same
exemplary trigger 1000 and camshaft 1060 of FIGS. 11 and 13
respectively with the trigger 1000 oriented in a disengagement
position. The trigger 1000 selectively rotates between the
engagement position of FIGS. 11 and 13 and the disengagement
position of FIGS. 12 and 14 so as to selectively engage the
associated lifter assembly 1080, 1090.
[0056] Selective rotation of the trigger 1000 can be achieved by
way of interplay between centripetal forces operating on
counterweight 1020 (when rotating) and spring forces operating on
spring engagement surfaces of trigger 1000/camshaft 1060 (at all
times). In particular, at all RPMs the spring 1040 provides a
relative force between the trigger 1000 and the camshaft 1060
tending to cause rotation of the trigger 1000 into the engaged
position and to hold the trigger 1000 therein. For example,
referring to FIG. 15, the spring 1040 tends to cause clockwise
rotation of trigger 1000 about pin 1010 based on the spring 1040's
application of a relative force between camshaft 1060 and trigger
1000. However, as the rotational velocity of the camshaft 1060
gradually increases, the centripetal forces acting on counterweight
1020 similarly gradually increase. These centripetal forces tend to
cause a rotation of trigger 1000 opposite the rotation caused by
spring 1040 (and, in some applications, opposite the rotation
caused by gravity with or without assistance by spring 1040).
Referring again to FIG. 15, the centripetal forces acting on
counterweight 1020 will tend to cause counterclockwise rotation of
trigger 1000 about pin 1010. At some known rotational velocity (and
at rotational velocities above this known value) that depends on
spring 140 parameters and trigger 1000 parameters, the torque on
trigger 1000 caused by centripetal forces acting on counterweight
1020 exceeds the torque caused by spring forces from spring 1040.
Thus, the trigger 1000 rotates from the engagement position toward
the disengagement position (i.e., from the orientation shown in
FIG. 11 to the orientation shown in FIG. 12). When the rotational
velocity falls below the known value (e.g., when the engine is
turned off), the torque caused by spring forces from spring 1040
again exceeds the torque caused by centripetal forces acting on
counterweight 1020, and the trigger 1000 rotates back toward the
engagement position from the disengagement position (i.e., from the
orientation shown in FIG. 12 to the orientation shown in FIG. 11).
In this manner, the trigger 1000 is selectively rotated between the
engagement position and the disengagement position.
[0057] Preferably, the compression release lobe 1030 of trigger
1000 and/or the camshaft lobe 1070 of camshaft 1060 are configured
to have peripheries that enhance operation of the compression
release mechanism. For example, as shown in FIGS. 25-30, the
compression release lobe 1030 may include a lifter roller
engagement surface (i.e., the surface that comes into contact with
lifter assembly 1080, 1090) arced between a first end and a second
end, both the first end and the second end being at about a same
fixed distance from the trigger axis 1015. Preferably, when the
trigger 1000 is positioned in the engagement position, the lifter
roller engagement surface arcs about the camshaft axis 1065. See,
for example, FIG. 24. Such an orientation allows the lifter
assembly 1080, 1090 to travel an arced path while in contact with
the lifter roller engagement surface. See, for example, FIG. 30 The
compression release lobe 1030 of trigger 1000 may also include
beveled edges extending along at least a portion of the lifter
roller engagement surface. Preferably, the compression release lobe
1030 of trigger 1000 at least includes beveled edges on those edges
extending between the first end and the second end of the
engagement surface described above.
[0058] According to an embodiment of the present invention, the
camshaft lobe 1070 includes a recess that receives the compression
release lobe 1030 when the trigger 1000 is in the engagement
position. As shown, for example, in FIG. 30, the recess may have a
sufficient volume to permit direct contact between the roller of
the lifter assembly 1080 and the lifter roller engagement surface
of compression release lobe 1030. As shown in FIGS. 16 and 30,
however, the recess may have a volume that only allows for part of
the roller of the lifter assembly 1080 to directly contact the
lifter roller engagement surface of compression release lobe 1030.
Stated another way, when the lifter assembly 1080 is in contact
with the trigger 1000, part of the lifter roller surface is in
contact with the lifter roller engagement surface and another part
of the lifter roller surface is free floating. This configuration
allows the base circle to remain intact for normal engine
operation, and the trigger 1000 to contact the lifter assembly
during low engine speeds as described in greater detail below.
[0059] Because the compression release lobe 1030 of trigger 1000
protrudes from the camshaft base circle when in the engaged
position, the compression release lobe 1030 contacts the lifter
assembly 1080, 1090 traveling the camshaft base circle. Contact
between the compression release lobe 1030 and the lifter assembly
1080, 1090 causes the lifter assembly 1080, 1090 to crack the
associated valve open. For example, a lifter assembly 1080, 1090
for an exhaust valve may be contacted during the compression stroke
to relieve a certain amount of cranking compression and thereby
allow the engine to start easier. Preferably, when contact between
the compression release lobe 1030 and the lifter assembly 1080,
1090 occurs, there is no contact between the lifter assembly 1080,
1090 and the camshaft lobe 1070.
[0060] It should be appreciated that the trigger 1000 is held in
the engaged position at RPMs below a known value due to the use of
a spring 1040 positioned between the trigger 1000 and the camshaft
1060 (or due to the presence of gravity, with or without assistance
by spring 1040). Preferably, a compression spring 1040 is utilized
with a known spring constant. Certain parameters of the compression
spring 1040, such as the spring constant, can be adjusted for a
given application at hand so as to correspondingly adjust the RPM
at which a given trigger 1000 will rotate from an engaged position
to a disengagement position and vice versa. Similarly, certain
parameters of the trigger 1000 (e.g., the amount of mass and
distribution thereof in counterweight 1020) can be adjusted for a
given application at hand so as to correspondingly adjust the RPM
at which the trigger 1000 will rotate from an engaged position to a
disengagement position and vice versa. By way of example, an
optional through hole 1025 may be provided in counterweight 1020 to
reduce the associated mass or the center of gravity thereof.
Through hole 1025 may also be used for manufacturing purposes.
[0061] The modifiability of the compression release mechanism
(and/or parameters thereof) described above is exemplified by the
embodiments shown in FIGS. 31-34, comparison FIG. 35, and/or
camshaft FIGS. 36-39. As shown, for example, in FIGS. 31-34, a
compression release mechanism may be provided in camshaft 10600
(which includes camshaft lobe 10700) which actuates a lifter
assembly 10800. The compression release mechanism shown includes a
trigger 10000 with compression release lobe 10300 and counterweight
10200, a pin 10100 about which the trigger 10000 rotates, and a
spring 10400 positioned between the camshaft 10600 and the trigger
10000. Operation of the compression release mechanism shown in
FIGS. 31-34 is substantially similar to operation of the
compression release mechanism(s) shown in FIGS. 8-30.
[0062] The compression release mechanism of FIGS. 31-34 differs
from the compression release mechanism(s) of FIGS. 8-30, however,
in several respects. In particular, the compression release
mechanism of FIGS. 31-34 has been modified to accommodate a
different engine family. As shown, for example, by comparing the
camshaft 10600 of FIGS. 36 & 37 with the camshaft 1060 of FIGS.
38, 39, different lifter assembly orientations are accommodated by
the profiles of the camshafts 1060 and 10600. Camshaft differences
include, for example, a change in diameter of about 0.150'',
shallower counterweight pockets in camshaft 10600 due to smaller
trigger counterweight 10200, simplification and enlargement of the
angled pockets in camshaft 10600 to speed machining processes, and
reorientation of the trigger counterweight 10200 to between
camshaft lobes.
[0063] Corresponding trigger 1000, 10000 differences can also be
observed by referencing the side by side comparison in FIG. 35. As
shown, the trigger 10000 includes a shorter nose part than trigger
1000 to accommodate the smaller camshaft diameter. Further,
counterweight 10200 is shortened and given a modified shape to
provide for lifter clearance due to the presence of two lifter
assemblies operating on the same camshaft 10600. Further, the
counterweight through hole in trigger 10000 is decreased in
diameter and moved so as to maximize the mass and movement of the
counterweight 10200. As shown in FIGS. 33 and 34, machining around
the nose of lobe 10300 was simplified and/or eliminated to reduce
machining time. Other variations may also exist as would be readily
understood by those of skill in the art after reading this
disclosure.
[0064] A compression release mechanism and associated camshaft
20600 according to yet another embodiment of the present invention
is shown in FIGS. 40-42. The compression release mechanism includes
a ring 20000 which rotates about a pin 20100 operably connected to
camshaft 20600. The ring 20000 includes a decompression lobe 20300
and a counterweight 20200. A spring 20400, such as a coil spring,
is operably attached to pin 20100 and counterweight 20200.
[0065] Operation of the compression release mechanism shown in
FIGS. 40-42 is analogous in at least some respects to operation of
the compression release mechanisms shown in FIGS. 8-39. In
particular, at low RPMs (e.g., during engine cranking), the spring
20400 applies a relative force between ring 20000 and camshaft
20600 so as to hold the release in an engagement position (FIG.
40). Once the camshaft 20600 achieves or exceeds a certain
rotational velocity, centripetal forces acting on counterweight
20200 overcome the force of the spring 20400 thereby causing ring
20000 to rotate from the engagement position shown in FIGS. 40 and
42 to the disengagement position shown in FIG. 41. A lifter
assembly (not shown) traveling along camshaft lobe 20700 will thus
contact lobe 20300 when ring 20000 is in the engagement position,
and will avoid contact with lobe 20300 when ring 20000 is in the
disengagement position.
[0066] It should be appreciated that camshaft lobe 20700 of
camshaft 20600 may include a periphery so as to accommodate lobe
20300 of ring 20000. As shown, for example, in FIG. 41, a region 2
of the camshaft lobe periphery is recessed relative to region 1 of
the camshaft lobe periphery. Region 1 includes a width
corresponding to the engagement portion of lobe 20300 as shown, for
example, in FIGS. 40 and 42. Other configurations are also
contemplated.
[0067] Referring now to the flowchart of FIG. 43, a method of
selectably releasing compression in an engine is shown. In step
5000, a compression release mechanism is provided with an internal
combustion engine. For example, step 5000 may comprise providing
the compression release mechanism of the embodiments shown in FIGS.
8-30 with an OEM twin cylinder motorcycle engine or retrofitting a
twin cylinder motorcycle engine to include such a compression
release mechanism. In step 5010, a trigger of the compression
release mechanism is held in an engagement position, e.g., by way
of a spring. Preferably step 5010 is performed at least while the
engine is turned off and while the engine is operating at RPMs
below a known value.
[0068] In step 5020, the trigger is rotated about a camshaft axis
at a rotational velocity. Step 5020 may be initiated, for example,
by a starter motor or kick starter of a motorcycle engine which
causes the engine to turn over at a relatively low RPM. While
operating at the relatively low RPM (e.g., at camshaft RPMs below
about three hundred and fifty RPMs or crankshaft RPMs below about
seven hundred RPMs), the trigger remains held in the engagement
position and a lifter assembly in the engine comes into contact in
step 5030 with a compression release lobe of the trigger. It should
be appreciated that "contact" in step 5030 refers to the periodic
contact once per revolution of the compression release lobe with
the lifter assembly. Contact in step 5030 with the lifter assembly
causes an associated valve to open slightly, thereby releasing
pressure in cylinder and allowing the engine to start more
easily.
[0069] Once the rotational velocity of the crankshaft achieves a
known value (e.g., at about engine idle or slightly below engine
idle), the trigger is rotated about a trigger axis in step 5040
from the engagement position toward a disengagement position. By
way of example, step 5040 can be performed by rotating a trigger
from the orientation shown in FIG. 11 to the orientation shown in
FIG. 12, or from the orientation shown in FIG. 13 to the
orientation shown in FIG. 14. In order to reduce the possibility of
the trigger being partially engaged when the trigger is in
transition (e.g., from an engagement position to a disengagement
position or vice versa), a profile of the trigger (e.g., of the
compression release lobe 1030 shown in FIGS. 25-30) can be designed
to include an arced surface and/or beveled edges.
[0070] While the trigger is oriented in the disengagement position,
the lifter assembly preferably contacts in step 5050 only the
camshaft lobe and not any portion of the trigger. To facilitate
this functionality, the trigger may be positioned within the
camshaft in the disengagement position such that a leading surface
is at or below a leading surface of an associated camshaft lobe.
Alternatively, a leading surface of the trigger may project beyond
a leading surface of an associated camshaft lobe provided the
trigger be positioned wholly outside the lifter assembly path of
travel.
[0071] When the rotational velocity of the camshaft falls below the
known value, such as during engine shutdown, the trigger is rotated
in step 5060 from the disengagement position toward the engagement
position. By way of example, step 5060 can be performed by rotating
a trigger from the orientation shown in FIG. 12 to the orientation
shown in FIG. 11, or from the orientation shown in FIG. 14 to the
orientation shown in FIG. 13.
[0072] As illustrated by the embodiments above, the present
invention can be used in a wide variety of applications. It should
be appreciated that various parameters, such as spring constants,
counterweight mass, counterweight center of mass, etc. may be
adjusted for a particular application at hand. By way of example,
one or more of the aforementioned embodiments can be used so as to
operate in an engagement position at RPMs below an RPM in a range
of about six hundred and twenty five crankshaft RPMs to about seven
hundred and twenty five crankshaft RPMs, or about half that for
camshaft RPMs. More preferably, one or more of the aforementioned
embodiments can be used so as to operate in an engagement position
at RPMs below about seven hundred crankshaft RPMs or about three
hundred and fifty camshaft RPMs. Other possibilities are also
contemplated.
[0073] The foregoing description of various embodiments of the
present invention has been presented for purposes of illustration
and description. It is not intended to be exhaustive or to limit
the invention to the precise form disclosed, and modifications and
variations are possible in light of the above teachings or may be
acquired from practice of the invention. The embodiments were
chosen and described in order to explain the principles of the
invention and its practical application to enable one skilled in
the art to utilize the invention in various embodiments and with
various modifications as are suited to the particular use
contemplated.
* * * * *