U.S. patent application number 14/870004 was filed with the patent office on 2016-01-21 for rocker arm assembly for valve actuation systems.
This patent application is currently assigned to Caterpillar Inc.. The applicant listed for this patent is Caterpillar Inc.. Invention is credited to James J. Cress.
Application Number | 20160017766 14/870004 |
Document ID | / |
Family ID | 55074178 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160017766 |
Kind Code |
A1 |
Cress; James J. |
January 21, 2016 |
ROCKER ARM ASSEMBLY FOR VALVE ACTUATION SYSTEMS
Abstract
A rocker arm assembly for a valve actuation system of an engine
is disclosed. The engine has at least one valve. The rocker
assembly includes a rocker arm with a valve retention end, a valve
bridge with a rocker engagement portion. The rocker engagement
portion sustains an engaged position and a released position
relative to the valve retention end. Further, a spring unit is
disposed between the valve retention end and the rocker engagement
portion. In the engaged position, the valve retention end is in
operable abutment with the rocker engagement portion. In the
released position, the spring unit is configured to provide a
reaction force between the valve retention end and the rocker
engagement portion to disconnect the valve bridge from the rocker
arm.
Inventors: |
Cress; James J.; (West
Lafayette, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Caterpillar Inc. |
Peoria |
IL |
US |
|
|
Assignee: |
Caterpillar Inc.
Peoria
IL
|
Family ID: |
55074178 |
Appl. No.: |
14/870004 |
Filed: |
September 30, 2015 |
Current U.S.
Class: |
123/90.39 |
Current CPC
Class: |
F01L 1/18 20130101; F01L
1/46 20130101 |
International
Class: |
F01L 1/18 20060101
F01L001/18; F01L 1/46 20060101 F01L001/46 |
Claims
1. A rocker arm assembly for a valve actuation system of an engine,
the engine including at least one valve, the rocker arm assembly
comprising: a rocker arm having a valve retention end; a valve
bridge having a rocker engagement portion, the rocker engagement
portion sustaining an engaged position and a released position
relative to the valve retention end; and a spring unit disposed at
an interface defined between the valve retention end of the rocker
arm and the rocker engagement portion of the valve bridge, wherein
in the engaged position the valve retention end is in operable
abutment with the rocker engagement portion, wherein in the
released position the spring unit is configured to provide a
reaction force between the valve retention end and the rocker
engagement portion to disconnect the valve bridge from the rocker
arm.
2. The rocker arm assembly of claim 1, wherein the spring unit
includes a first biasing member extended laterally from the valve
retention end and a second biasing member extended diametrically
oppositely to the first biasing member, wherein the first biasing
member defines a first remote curvature portion and the second
biasing member defines a second remote curvature portion, with both
the first remote curvature portion and the second remote curvature
portion being resiliently resting about an outer surface of the
valve bridge, in the engaged position.
3. The rocker arm assembly of claim 1, wherein the valve bridge
includes a pocket and the spring unit is a resilient member, with
at least a portion of the resilient member being disposed within
the pocket and an opposed end of the resilient member being in
abutment with the valve retention end.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to rocker arm
assemblies in internal combustion engines. More specifically, the
present disclosure relates to a mechanism to overcome a sticking
force between a valve bridge and a rocker arm of the rocker arm
assemblies, during excessive lash conditions, by use of a spring
unit.
BACKGROUND
[0002] Several applications related to internal combustion engines
in the construction machine industry involve rigorous operational
cycles for valve trains. Therefore, valve trains are required to
exhibit exceptional quality, reliability, and prolonged life. As a
result, stupendous effort and resources have been invested in
optimizing the working of components, such as rocker arms in valve
trains, and in their associated connection to the valves.
Conventionally, floating bridges have been applied as an
interfacial connector between a rocker arm and a valve stem, in
valve train assemblies. Floating bridges are generally positioned
freely over associated valve stems, while also being relatively
non-restrictively positioned in relation to the rocker arm.
[0003] Typically, valve units in valve trains are subject to lash
conditions. A lash condition arises from an existential clearance
between the rocker arm and a valve tappet. Such clearances are
commonly provided to accommodate for thermal expansion in the
components. While lash conditions are suitably arrested by the
incorporation of widely available lash adjusters, such as hydraulic
lash adjusters, a misadjusted valve train, unfilled hydraulic lash
adjusters, or a fully collapsed hydraulic lash adjuster, may result
in an inappropriate containment of lash. In such situations, the
rocker arm may sustain an increased clearance from the valve
tappet. Given the occupancy of lubrication oil in the immediate
vicinity of the valve train, floating bridges have a tendency to
adhere to the rocker arm and be retained by the rocker arm because
of the surface tension and a resulting `sticking force` induced by
an amount of lubrication oil present therebetween. As a result,
during a released state of the valves, the floating bridge may
stick to the rocker arm and be dislodged from the valve stem. In a
cyclical process, such a phenomenon may lead to a condition where
floating bridges fail to appropriately return to the valve stem,
leading to a dropped valve and a failure in the timely intake of
air or ejection of exhaust gases.
[0004] WIPO Application 2014/001560 A1 relates to a valve bridge
for use in a valve train assembly that provides a brake function in
compression engines. Although the '560 reference discloses the use
of springs in lash adjusters, no solution is provided that could
limit the adherence or retention of the valve bridge, or the
floating bridge, to the rocker arm.
[0005] Accordingly, the system and method of the present disclosure
solves one or more problems set forth above and other problems in
the art.
SUMMARY OF THE INVENTION
[0006] Various aspects of the present disclosure illustrate a
rocker arm assembly for a valve actuation system of an engine. The
engine includes at least one valve. The rocker arm assembly
includes a rocker arm having a valve retention end. A valve bridge
has a rocker engagement portion that sustains an engaged position
and a released position relative to the valve retention end. A
spring unit is disposed at an interface between the valve retention
end of the rocker arm and the rocker engagement portion of the
valve bridge. In the engaged position, the valve retention end is
in operable abutment with the rocker engagement portion. In the
released position, the spring unit is configured to provide a
reaction force between the valve retention end and the rocker
engagement portion to disconnect the valve bridge from the rocker
arm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view of a rocker arm assembly
for a valve actuation system in an internal combustion engine that
illustrates an exemplary connection between a rocker arm and a
valve bridge, in accordance with the concepts of the present
disclosure;
[0008] FIG. 2 is a cross-sectional view of the valve bridge,
depicting an embodiment of a spring unit disposed at an interface
between the valve bridge and the rocker arm, in accordance with the
concepts of the present disclosure; and
[0009] FIG. 3 is a cross-sectional view of another embodiment of
the valve bridge, depicting an auxiliary spring unit disposed
between the valve bridge and the rocker arm, in accordance with the
concepts of the present disclosure.
DETAILED DESCRIPTION
[0010] Referring to FIG. 1, there is shown an exemplary rocker arm
assembly 10 for a valve actuation system 12 of an internal
combustion engine 14. The internal combustion engine 14 may be
interchangeably referred to as an engine 14. The engine 14 may be
utilized in a construction machine (not shown) such as an
excavator, a loader, a forest machine, a marine machine, Large
Mining Trucks (LMTs), and other similar machines. In an embodiment,
the engine 14 is a four-stroke engine in which a piston (not shown)
executes four strokes of operation (an intake stroke, a compression
stroke, a combustion stroke, and an exhaust stroke), in one
thermodynamic cycle. The engine 14 may embody a single cylinder or
a multi-cylinder configuration. Moreover, the engine 14 may include
any of the conventionally available configurations, such as an
inline configuration, V-type, and similar other conformations. An
extension of the application of the present disclosure may be
extended to engines of generator sets employed in commercial and
domestic establishments.
[0011] The rocker arm assembly 10 is envisioned to facilitate
allowance of a quantity of air into a combustion chamber (not
shown) of the engine 14 to support combustion. Alternatively, it
may be contemplated that the rocker arm assembly 10 is abled to
relieve the engine 14 of the exhaust gases, produced as by-products
of combustion, as well. However, the present disclosure envisions
the application of the rocker arm assembly 10 to be directed
towards a pair of intake valves 16 of the engine 14 alone, but it
may be well suited for one to apply and execute a similar
arrangement for a set of exhaust valves (not shown) in single or
multi-cylinder configurations. The rocker arm assembly 10 includes
the pair of intake valves 16, a rocker arm 18, a rocker shaft 20,
and a valve bridge 24.
[0012] The intake valves 16 embody two tappet valves as shown. The
intake valves 16 are generally supported in a cylinder head of the
engine 14. The cylinder head is not shown for clarity. The intake
valves 16 are adapted to linearly reciprocate and switch between an
open position and a closed position relative to the engine 14. In
the open position, the intake valves 16 allow air to flow into the
combustion chamber (not shown) of the engine 14. In the closed
position, the intake valves 16 restrict the flow of the air to the
combustion chamber (not shown) of the engine 14. Intake valves 16
include valve stems 26 that are engaged with the valve bridge 24.
Although, the present disclosure contemplates the inclusion of
tappet valves, various other types of intake valves may be
contemplated. Moreover, aspects of the present disclosure are
equivalently applicable to single valve and single cylinder
applications, as well.
[0013] The rocker arm 18 is rotatably mounted on the rocker shaft
20. The rocker arm 18 is cam operated. The rocker arm 18 includes a
cam attachment end 28 and a valve retention end 30. The cam
attachment end 28 is connected to a cam lobe 32 via a follower link
34. The valve retention end 30 of the rocker arm 18 is connected to
the intake valves 16 by the valve bridge 24. A rotational movement
of the cam lobe 32 corresponds to an oscillatory movement of the
rocker arm 18, which correspondingly facilitates the switch of the
intake valves 16 between the open position and the closed position,
relative to the engine 14. The valve retention end 30 of the rocker
arm 18 includes a ball and socket joint 36, with a ball portion 38
and a socket portion 40. The rocker arm 18 includes an internal
threaded opening 37 provided at the valve retention end 30 to
receive the ball and socket joint 36. To this end, the socket
portion 40 has an external threaded portion 41 provided to engage
with the internal threaded opening 37 of the rocker arm 18.
[0014] The ball and socket joint 36 is threadably connected to the
rocker arm 18 at the valve retention end 30. The ball portion 38
includes a surface 42, which faces the valve bridge 24. The surface
42 is a generally flat smoothened surface enabled for abutment to
the valve bridge 24.
[0015] The valve bridge 24 is a generally interfacial connector
between the rocker arm 18 and the intake valves 16. The valve
bridge 24 includes a rocker engagement portion 44 that is generally
freely placed, but is in operable abutment relative to the valve
retention end 30 (or the surface 42 of the ball portion 38) of the
rocker arm 18, during operations. An engagement of the valve bridge
24 with the intake valves 16 is facilitated by valve recesses 46
(best seen in FIGS. 2 and 3) that are provided at a surface of the
valve bridge 24, facing towards the valve stems 26. The valve
recesses 46 are able to slidably receive a portion of the valve
stems 26, but remain in an unlocked state relative to the valve
stems 26. As a result, the valve bridge 24 may be considered as a
floating bridge, which is neither fully constrained by the valve
retention end 30 of the rocker arm 18, nor fully restricted by the
valve stems 26. The valve bridge 24 sustains an engaged position
and a released position relative to the valve retention end 30 of
the rocker arm 18. In the engaged position, the intake valves 16
are pushed against valve springs 48 and thereby the intake valves
16 are opened relative to the engine 14 to allow the air to flow
into the engine 14. In the released position, conversely, the
intake valves 16 are released from the engaged position and are
closed relative to the engine 14, so as to restrict the
introduction of the air into the engine 14.
[0016] Generally, the valve bridge 24 is a triangular, pyramidal,
or prism shaped component, but other shapes, such as cuboidal
shapes, may be contemplated. The operable abutment between the
valve retention end 30 of the rocker arm 18 and the rocker
engagement portion 44 of the valve bridge 24 is but a surficial
contact between the two.
[0017] The valve retention end 30 includes a smoothened flat
surface defined by the surface 42 of the ball portion 38, which is
obtainable by conventional machining operations. Similarly, the
rocker engagement portion 44 is a smoothened flat surface, which is
able to contact the valve retention end 30, in a complementary
fashion, during operations.
[0018] The rocker arm assembly 10 is surrounded by a lubricant. The
lubricant provides sufficient ease in the movement and functioning
of the intake valves 16, the rocker arm 18, and surrounding
components, in varied degrees of motion, as is customary. As a
result, the rocker engagement portion 44 and the valve retention
end 30 are exposed to the lubricant, and, thus, the rocker
engagement portion 44 is subject to an amount of a lubricant-based
adhesive force relative to the valve retention end 30. However, the
lubricant-based adhesive force may vary according to the surface
tension and other characteristics exhibited by the applied
lubricant.
[0019] Referring to FIGS. 1, 2 and 3, the rocker arm assembly 10 is
inclusive of a spring unit 50, disposed relative to the valve
bridge 24. More particularly, the spring unit 50 is disposed at an
interface defined between the valve retention end 30 of the rocker
arm 18 and the rocker engagement portion 44 of the valve bridge 24.
In the engaged position, the spring unit 50 allows operable
abutment between the valve retention end 30 of the rocker arm 18
and the rocker engagement portion 44 of the valve bridge 24. In the
released position, however, the spring unit 50 is adapted to impart
a reaction or a counter force substantially higher than the
lubricant-based adhesive force, existing between the valve
retention end 30 and the rocker engagement portion 44 so as to
separate the valve bridge 24 from the rocker arm 18.
[0020] Referring to FIG. 2, an enlarged view of the spring unit 50
is depicted. The spring unit 50 is of a leaf spring type, which is
inclusive of a first biasing member 52 and a second biasing member
54. Both the first biasing member 52 and the second biasing member
54 are connected fixedly to the valve retention end 30 of the
rocker arm 18. A general assembly of the first biasing member 52
and the second biasing member 54 to the valve retention end 30 may
be attained threadably. For example, the first biasing member 52
and the second biasing member 54 are connected with the socket
portion 40, which is in turn threadably connected with the valve
retention end 30. An assembly of the spring unit 50 is performed
during an assembly of the rocker arm 18 with the ball and socket
joint 36. In general, the valve retention end 30 may include a
threaded stud (not shown) to which the spring unit 50 is first
threadably assembled. Thereafter, the ball and socket joint 36 is
threadably and successively secured to the valve retention end
30.
[0021] The first biasing member 52 extends substantially laterally
from the valve retention end 30 of the rocker arm 18, while the
second biasing member 54 extends diametrically oppositely to the
first biasing member 52 from the valve retention end 30. Both the
first biasing member 52 and the second biasing member 54 include an
S-shaped profile. Accordingly, each of the first biasing member 52
and the second biasing member 54 includes a splined shaped
dual-curvature design. First curvatures of both the first biasing
member 52 and the second biasing member 54 are defined relatively
closely to the valve retention end 30, upon an assembly of the
spring unit 50 with the rocker arm 18. Second curvatures of each of
the first biasing member 52 and the second biasing member 54 are
defined at a first remote curvature portion 56 and a second remote
curvature portion 58. When viewed collectively, the spring unit 50
resonates the profile of an inwardly positioned cup-shaped member,
as the first biasing member 52 and the second biasing member 54 are
symmetrical to each other when deployed. In the engaged position
between the rocker arm 18 and the valve bridge 24, both the first
remote curvature portion 56 and the second remote curvature portion
58 are disposed relatively resiliently about an outer surface 60 of
the valve bridge 24 in the engaged position, in order to assume an
expanded state of the spring unit 50.
[0022] Both the first biasing member 52 and the second biasing
member 54 form portions of an integrally formed spring unit 50. In
an embodiment, the first biasing member 52 may be a separately
formed component, and may be assembled to the second biasing member
54, during an assembly to the valve retention end 30. In principle,
a combination of both the first biasing member 52 and the second
biasing member 54 is set to act as a leaf spring against the outer
surface 60 of the valve bridge 24. This arrangement is configured
to provide resilience to the rocker arm 18 against the valve bridge
24, and serve a counter action against the lubricant-based adhesive
force. Therefore, in the engaged position, the spring unit 50 in an
expanded state and in the released state the spring unit 50 is in a
retracted state.
[0023] Referring to FIG. 3, there is shown another embodiment of a
spring unit 50' that helps attain a requisite value of resilience
between the rocker arm 18 and a valve bridge 24' to counter the
lubricant-based adhesive force. The embodiment includes the use of
a resilient member, such as helical spring, which is positionable
between the rocker engagement portion 44 of the valve bridge 24'
and the valve retention end 30 of the rocker arm 18, as shown. To
retain the spring unit 50' at the interface, the valve bridge 24'
is provided with a pocket 62 at the rocker engagement portion 44.
At least a portion of the spring unit 50' is disposed within the
pocket 62, while an opposed end 64 of the spring unit 50' is in
substantial abutment with the valve retention end 30. In that
manner, a degree of resilience is obtained between the valve bridge
24 and the rocker arm 18. The pocket 62 is structured to
accommodate and position the spring unit 50' along a line of
action, A, of the valve retention end 30 that acts against the
rocker engagement portion 44, during operations. Other features of
the valve bridge 24' remain similar to the valve bridge 24.
[0024] In an embodiment, the spring unit 50' is freely positioned
within the pocket 62, while it is also possible that the pocket 62
includes measures that fixedly retain the spring unit 50' within
the pocket 62. As an example, industrial adhesives, brazing, and
the like, may be contemplated to establish such a retention.
[0025] In another embodiment, the resilient member (or spring unit
50') is a Belleville washer (not shown). This is because Belleville
washers generally possess a frusto-conical shape, which imparts a
spring characteristic to the Belleville washers. As with the
helical spring, a Belleville washer may be positionable between the
valve retention end 30 and the rocker engagement portion 44, with a
portion of the Belleville washer being positioned within the pocket
62, and an opposed end of the Belleville washer standing in
abutment against the valve retention end 30. A convergent end of
the Belleville washer may be positioned against the valve retention
end, while a divergent end of the Belleville washer may be in
abutment with the rocker engagement portion.
INDUSTRIAL APPLICABILITY
[0026] Generally, the working of the rocker arm assembly 10
involves the use of lubricant within an immediate vicinity. As a
result, the components of the rocker arm assembly 10 are exposed to
the lubricant. Since the surfaces (surface 42) defined by the valve
retention end 30 and the rocker engagement portion 44 are generally
smooth, flat, and considerably in periodic contact with each other,
it becomes increasingly possible that the two surface bond with
each other because of the presence of an amount of the lubricant
in-between. This causes the valve bridge 24 to stick to the valve
retention end 30 of the rocker arm 18, during each event of the
release position. Given repeated operations, a dislodgement of the
valve bridge 24 from the valve stems 26, during excessive lash
conditions, becomes more and more possible.
[0027] Conditions that additionally factor in the adherence of the
valve retention end 30 with the rocker engagement portion 44 is the
general characteristics of the lubricant. For example, a relatively
highly viscous lubricant may exhibit a different adherence
capability than a lubricant, which is relatively less viscous.
Moreover, the temperature at which the lubricant operates may
decide the `sticking force` observed between the valve retention
end 30 and the rocker engagement portion 44.
[0028] During operations, the rocker arm 18 shifts between two
operable positions. The first position is the engaged position,
while the second position relates to the released position. Both
these positions of the rocker arm are defined relative to the valve
bridge 24. In the engaged position, the rocker arm 18 swings to
push the valve bridge 24, and in so doing, the rocker arm 18 pushes
the intake valves 16 to define an open position relative to the
internal combustion engine (ICE) 14. In the released position, the
rocker arm 18 releases the valve bridge 24 from the state of being
pushed, so as to allow a freely obtained closure of the intake
valves 16. Excessive lash conditions or conditions that result from
an inappropriately contained lash impart excessive clearances
between the rocker arm 18 and the valve bridge 24. Because of the
presence of lubricant between the valve retention end 30 and the
rocker engagement portion 44, a `sticking force` or the
`lubricant-based adhesive force` between the rocker arm 18 and the
valve bridge 24 forces the valve bridge 24 out of engagement with
the valve stems 26. At this point, the spring unit 50, 50' disposed
at the interface between the valve bridge 24 and the rocker arm 18
imparts a counter force against the lubricant-based adhesive force
and avoids a disengagement of the valve bridge 24 from the valve
stems 26. This counter force imparts a degree of separation and
maintains a minimum clearance between the valve retention end 30 of
the rocker arm 18 and the rocker engagement portion 44 of the valve
bridge 24, in the event of an existence of lash in the rocker arm
assembly 10.
[0029] During use of the spring unit 50, the counter force is
imparted about a characteristic curve sustained simultaneously at
the first remote curvature portion 56 and the second remote
curvature portion 58 of the spring unit 50. Conversely, in the
event of an application of spring unit 50', a counter force is
induced generally along a linear line of action, A, (FIG. 3) of the
push imparted by the rocker arm 18 to the valve bridge 24.
[0030] The aspects of the present disclosure may operate in the
absence of one or more components. Further, properties of the
spring unit 50, 50', such as the spring constant, and the like, may
vary from application to application. Variations that includes the
usage of differently configured springs applied between the rocker
arm 18 and the valve bridge 24 fall within the ambit of the present
disclosure. Moreover, although the present embodiment discloses the
use of the valve bridge as a floating bridge, specifications of the
present disclosure may be equivalently applicable for a guided
bridge.
[0031] It should be understood that the above description is
intended for illustrative purposes only and is not intended to
limit the scope of the present disclosure in any way. Thus, one
skilled in the art will appreciate that other aspects of the
disclosure may be obtained from a study of the drawings, the
disclosure, and the appended claim.
* * * * *