Rocker Arm Assembly With Lost Motion for Engine Braking
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Solution Overview
Problem
Existing rocker arm systems in compression engine brakes face issues with hydraulic lash adjusters extending undesirably during engine braking, leading to loss of compression and potential piston-to-valve contact due to the cocked valve bridge.
Innovation Solution
A rocker arm assembly with integrated hydraulic lash adjuster and lost motion mechanism, featuring a movable lever assembly that prevents unintended extension of the hydraulic lash adjuster during braking, allowing selective engagement of engine valves for both exhaust and engine braking events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a hydraulic lash adjuster is used in the rocker arm assembly, then lash adjustment is automated and maintenance is reduced, but the hydraulic lash adjuster extends undesirably during engine braking causing loss of compression
Solution Approach 1:
The rocker arm assembly is segmented into distinct functional zones: a first portion for normal valve actuation and a second portion for engine braking. The hydraulic lash adjuster is isolated to the first portion, while the second portion uses a separate actuation mechanism with its own cam surface, preventing the lash adjuster from interfering with engine braking compression retention.
Solution Approach 2:
The harmful extension behavior of the hydraulic lash adjuster is extracted and isolated from the engine braking function. By creating a separate second portion of the rocker arm with dedicated engine braking actuation, the lash adjuster's unwanted movement is prevented from affecting compression during braking events.
2Device complexity
If the rocker arm is designed for single function (normal operation), then the structure is simple, but it cannot perform both valve actuation and engine braking functions
Solution Approach 1:
The rocker arm assembly is designed as a multi-functional universal component. The first portion handles normal valve actuation with the hydraulic lash adjuster, while the second portion provides engine braking function with a separate cam surface and actuation mechanism. This allows a single rocker arm assembly to perform both exhaust valve actuation and engine braking operations.
Solution Approach 2:
The rocker arm assembly dynamically adapts its function based on operational mode. The presence of both a first cam surface for normal operation and a second cam surface for engine braking allows the system to switch between functions. The separate actuation paths enable the rocker arm to respond differently to cam lobes depending on whether normal valve actuation or engine braking is required.
3Ease of operation
If the hydraulic lash adjuster is allowed to extend during braking, then the valve bridge can cock to engage the brake cam, but compression is lost and piston-to-valve contact may occur
Solution Approach 1:
The design preliminarily prevents the harmful extension of the hydraulic lash adjuster during engine braking by providing a separate second portion of the rocker arm dedicated to braking actuation. This preliminary prevention eliminates the need for the valve bridge to cock and avoids the harmful consequences of compression loss and potential piston-to-valve contact.
Solution Approach 2:
A separate second cam surface and actuation mechanism serve as an intermediary for engine braking operations. This intermediary system handles the braking function independently, preventing the hydraulic lash adjuster from being involved in the braking process and thus preventing compression loss while still enabling proper brake cam engagement.
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
The solution effectively manages lash adjustment and prevents unwanted valve extension during engine braking, maintaining optimal engine performance and reducing actuation force requirements.
Implementation Method 1
a hydraulic capsule configured to selectively move from a collapsed state to an expanded state to transfer cam motion to the valve bridge assembly
Implementation Method 2
a lost motion mechanism configured to absorb rocker arm motion during engine braking events
Data Source
AI summary
A rocker arm configured to perform a first event and a second event against a valve bridge assembly operably associated with first and second engine valves includes a rocker arm body configured to rotate about a rocker shaft. The rocker arm body includes a first event rocker arm assembly comprising a hydraulic capsule in a bore, and a second event rocker arm assembly. The first event rocker arm assembly is configured to selectively engage the valve bridge assembly to open the first and second engine valves.