Valve Train Rocker Arm Biasing for Engine Brake Lash Control
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Solution Overview
Problem
The existing valve train assemblies for engine brake functionality suffer from excessive mechanical lash between the engine brake lift cam and exhaust valves, leading to noise and wear, especially when the engine brake capsule is in the retracted position, which disables engine braking and allows rocker arms to tilt freely.
Innovation Solution
The introduction of biasing assemblies with levers, lost motion springs, and limiting means for rocker arms following the engine brake lift cam, which bias the rocker arms to a default position, accommodate mechanical lash, and prevent free tilting, along with lash adjustment screws and compliance springs to optimize operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the engine brake capsule is in retracted position to disable engine braking, then normal engine operation is enabled, but the rocker arm can tilt freely causing noise and wear
Solution Approach 1:
The biasing assembly applies a preliminary counteracting force to the rocker arm through the lever and spring mechanism, preventing free tilting motion before harmful noise and wear can occur. The limiting means further constrains the lever rotation to ensure the rocker arm remains controlled during engine brake capsule retraction.
2Reliability
If the engine brake capsule is in extended position to enable engine braking, then compressed air release is enabled, but excessive mechanical lash between cam and valve remains
Solution Approach 1:
The biasing assembly acts as an intermediary mechanism between the rocker arm and the engine brake capsule, providing continuous positional control through the lever and spring system. This intermediary mechanism fills the gap created by mechanical lash, ensuring the rocker arm maintains proper position even when the engine brake capsule is extended.
3Device complexity
If traditional valve train design is used without biasing assemblies, then device complexity is low, but rocker arms cannot be controlled in retracted position
Solution Approach 1:
The valve train system is segmented by adding independent biasing assemblies to specific rocker arms that follow engine brake lift cams. This segmentation allows selective control of rocker arm position only where needed (on the engine brake side), rather than controlling all rocker arms, thus balancing complexity and reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces noise and wear by ensuring rocker arms remain in a controlled position, maintaining engine braking functionality while allowing for efficient operation during normal engine operation and engine brake modes.
Implementation Method 1
a lost motion spring arranged between the lever and the rocker arm to accommodate mechanical lash
Implementation Method 2
each biasing assembly comprises a lever pivotably arranged on the top of the rocker arm... with which said one of the rocker arms is biased to a default position
Data Source
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AI summary
The invention relates to a valve train assembly comprising: at least a number of exhaust valves; at least one camshaft with at least a pair of a primary lift cam and an engine brake lift cam; a number of rocker arms (8, 9, 21), each having a cam follower for following one of the primary lift cam and the engine brake lift cam; wherein each rocker arm (21) having a cam follower following an engine brake lift cam is provided with an engine brake capsule; a number of biasing assemblies (30, 44) each one cooperating with one of the rocker arms of which the cam follower follows an engine brake lift cam to accommodate mechanical lash.