Valve Train Rocker Arm Biasing for Engine Brake Lash
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Solution Overview
Problem
The existing valve train assemblies for engine brake functionality suffer from excessive mechanical lash, leading to noise and wear due to the rocker arms tilting freely when the engine brake capsule is in the retracted position, which disables engine braking and causes inefficiencies.
Innovation Solution
The implementation of biasing assemblies that cooperate with rocker arms following the engine brake lift cam to accommodate mechanical lash, ensuring the rocker arms are biased to a default position, reducing noise and wear by using components like lost motion springs, lash adjustment screws, and compliance springs to manage the tilting movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the engine brake capsule is in the retracted position to disable engine braking, then normal engine operation is enabled, but the rocker arm tilts freely causing noise and wear
Solution Approach 1:
A biasing assembly is introduced as an intermediary component between the rocker arm and the engine brake lift cam. This biasing assembly maintains continuous contact and applies a biasing force to keep the rocker arm in a default position, eliminating free tilting movement and the associated noise and wear, while still allowing the engine brake capsule to selectively enable or disable engine braking functionality.
2Productivity
If the engine brake capsule is in the extended position to enable engine braking, then compressed air release is enabled, but excessive mechanical lash remains causing rocker arm instability
Solution Approach 1:
The biasing assembly is pre-configured to apply a continuous biasing force to the rocker arm, establishing a default position before engine braking is activated. This preliminary action ensures that when the engine brake capsule is in the extended position, the rocker arm is already stabilized and properly positioned, eliminating excessive mechanical lash and ensuring stable operation during engine braking.
3Ease of operation
If the rocker arm is allowed to tilt freely to accommodate mechanical lash, then normal operation is simplified, but noise and wear increase significantly
Solution Approach 1:
The biasing assembly changes the mechanical parameters of the rocker arm system by applying a continuous biasing force that maintains optimal contact pressure between the rocker arm and the engine brake lift cam. This parameter change eliminates excessive clearance and mechanical lash while preserving the necessary rocker arm tilting movement for normal operation, thereby reducing noise and wear without compromising operational ease.
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 effectively reduces noise and wear by maintaining the rocker arms in a controlled position, ensuring efficient operation of the valve train assembly during both normal engine operation and engine brake modes, while providing the necessary engine braking functionality.
Implementation Method 1
a number of biasing assemblies each one cooperating with one of the rocker arms of which the cam follower follows an engine brake lift cam to accommodate mechanical lash. With the biasing assemblies the rocker arms with the cam follower following the engine brake lift cam is biased to a default position
Implementation Method 2
components like lost motion springs, lash adjustment screws, and compliance springs to manage the tilting movement
Implementation Method 3
a friction element arranged between the rocker arm and said pivot axis. The friction element prevents any free tilting movement of the rocker arm
Data Source
AI summary
A valve train assembly includes 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 each include a cam follower for following one of the primary lift cam and the engine brake lift cam. One rocker arm includes a cam follower following an engine brake lift cam. The rocker arm is provided with an engine brake capsule. Various biasing assemblies are disclosed that cooperate with one of the rocker arms of which the cam follower follows an engine brake lift cam to accommodate mechanical lash.