Roller Finger Follower Torsional Spring Relocation
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Solution Overview
Problem
Existing switchable roller finger followers in overhead cam type internal combustion engines face challenges in maintaining contact between the cam and cam follower during unlocked periods, leading to inefficiencies and reduced lifespan due to the placement of lost motion springs.
Innovation Solution
The lost motion torsional spring device is relocated to the lash adjuster end of the finger follower, utilizing two coaxial helical spring parts with long and short legs, secured by pins and a stop, and mounted on the outer housing with pallets providing a rolling contact surface to reduce wear and increase lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lost motion spring is placed in the conventional position within the finger follower body, then the spring can maintain contact between the cam and cam follower, but the mass moment of inertia about the pivot axis increases reducing operational efficiency
Solution Approach 1:
The lost motion spring is extracted from the conventional position within the finger follower body and relocated to the lash adjuster end, positioned above the lash adjuster. This extraction removes the spring's mass from the rotating portion of the mechanism, thereby reducing the mass moment of inertia about the pivot axis while the spring continues to perform its function of maintaining cam contact during unlocked periods
2Reliability
If the lost motion spring undergoes large angular deflection to maintain cam contact, then contact is maintained, but the spring lifespan is reduced due to increased wear and stress
Solution Approach 1:
The spring is repositioned from a conventional radial mounting to a longitudinal orientation along the finger follower's long axis. This dimensional change in spring placement allows the spring to maintain cam contact through a different geometric configuration that reduces the angular deflection required, thereby extending spring lifespan while maintaining reliable cam contact
3Duration of action of stationary object
If the spring is positioned to minimize angular deflection and maximize lifespan, then spring durability increases, but the ability to maintain effective cam contact may be compromised
Solution Approach 1:
The spring is positioned to act as an intermediary element between the lash adjuster and the cam-follower interface. By placing the spring at the lash adjuster end with its longitudinal orientation, it serves as a mediator that can maintain cam contact with minimal deflection, thereby extending spring lifespan while preserving cam contact effectiveness through its strategic intermediary position
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 configuration reduces the mass moment of inertia about the pivot axis, enhances the lifespan of the spring by minimizing angular deflection, and maintains effective cam contact, improving the operational efficiency and durability of the finger follower.
Implementation Method 1
a lost motion torsional spring device having two helical parts, one of each of said helical parts on one of each of said lost motion pins, each of said helical parts having a short leg and a long leg
Implementation Method 2
The pallets provide a contact surface for the long legs while the stop provides a contact surface for the short legs
Data Source
AI summary
The finger follower has an inner and outer body and a torsional lost motion spring positioned at its lash adjuster end of the outer body. The torsional lost motion spring has two helical parts each with a short leg that abuts the outer body and a long leg that contacts the inner body. The torsional spring is located above the pivot point of the finger follower so as to provide a low mass moment of inertia and to reduce the weight over the valve stem end of the follower.