US20160017766A1

US20160017766A1 - Rocker arm assembly for valve actuation systems

Info

Publication number: US20160017766A1
Application number: US14/870,004
Authority: US
Inventors: James J. Cress
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2015-09-30
Filing date: 2015-09-30
Publication date: 2016-01-21
Also published as: CN206221015U

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.

Description

TECHNICAL FIELD

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

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.
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.
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.
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

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

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;

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

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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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

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.
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.
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.
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.
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.
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.

Claims

What is claimed is:

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.