Switching Roller Finger Follower Stop Pin for Starting Position Lash
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Solution Overview
Problem
Existing overhead cam switching roller finger followers face challenges in setting the starting position due to variances in spring strength and tolerance stack up, making it difficult to accommodate these variations effectively.
Innovation Solution
A stop pin design with a select fit for size is implemented to manage lash and set the starting position, allowing for adjustable lash adjustment by using stop pins of varying diameters to accommodate different customer applications, and a clearance fit to prevent sticking during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spring is used to bias the inner arm to a starting position, then the inner arm returns to the starting position, but it is difficult to set the starting position due to variances in spring strength and tolerance stack up
Solution Approach 1:
The patent applies parameter changes by providing stop pins with different diameters (e.g., 0.250 inches, 0.252 inches, 0.254 inches) to adjust the starting position of the inner arm. This allows manufacturers to select the appropriate stop pin diameter to compensate for variances in spring strength and tolerance stack up, thereby achieving consistent starting positions without complex adjustment mechanisms.
2Manufacturing precision
If a stop pin is provided for limiting relative rotation, then the starting position can be limited, but it does not accommodate variances in spring strength and tolerance stack up
Solution Approach 1:
The stop pin design provides multi-functionality by serving both as a positional limiter and as an adjustable parameter for accommodating variances. The stop pin with selectable diameters allows the same component design to be used across different applications and tolerance scenarios, making the system universally applicable while maintaining precision.
Solution Approach 2:
By changing the diameter parameter of the stop pin, the system can adapt to different spring strengths and tolerance stack up conditions. This parameter adjustment allows the stop pin to accommodate variances while maintaining its function of limiting relative rotation to a precise starting position.
3Ease of operation
If a clearance fit is used for the stop pin, then sticking during operation is prevented, but lash adjustment precision may be reduced
Solution Approach 1:
The clearance fit applies local quality by providing a specific clearance between the stop pin and its housing only at the critical interface where sticking would occur. This localized clearance prevents sticking during operation while the precise diameter selection of the stop pin maintains lash adjustment precision at the functional interface with the inner arm.
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 enables precise adjustment of the starting position, reduces scrap and manufacturing costs, and maintains consistent performance by accommodating variances in spring strength and tolerance stack up, while minimizing part count and scrap.
Implementation Method 1
A stop pin, select fit for size to manage lash and set a starting position, contacts shoulders on both inner sides of the outer arms
Implementation Method 2
The stop pin can be assembled in the SRFF as by drop-in assembly through bores in-line with the shoulders and is crowned on the ends to prevent sticking during operation
Implementation Method 3
A spring biases an inner arm assembly with respect to outer arms so that the inner arm assembly returns to a starting position
Data Source
Figure 1~2
Figure 3~5
AI summary
A switching roller finger follower comprises an inner arm assembly. A pair of outer arms surround the inner arm assembly. A pivot axle connects the inner arm assembly to pivot with respect to the pair of outer arms from a starting position to a lost motion position. A latch assembly comprises a latch selectively movable from a latched position latching the inner arm assembly to move dependent with the outer arms and an unlatched position unlatching the inner arm assembly to pivot independent of the outer arms. A stop pin spans between the pair of outer arms and through an inner port in an axle of inner arm assembly. The stop pin comprises a clearance fit with the inner port, and the stop pin is configured pivotable independent of the outer arms. At least one return spring biases the stop pin toward the starting position.