Antirotated Piston Rack for Air Starter Valves
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Solution Overview
Problem
Existing manual wrench drives for air starter valves lack a mechanism to prevent relative rotation between the rack and the shaft during manual operation, which can lead to unintended valve position changes.
Innovation Solution
A tab with a flat surface is positioned between the valve skirt and the rack teeth, supported by a rack support with ears that engage the tab's flat surface to prevent relative rotation, ensuring axial movement without rotation when driven by a pinion gear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the rack is machined into a cylindrical portion of the shaft allowing rotation, then the valve skirt, shaft, and rack can rotate relative to the housing for manual operation, but relative rotation between the rack and shaft occurs during manual operation causing unintended valve position changes
Solution Approach 1:
A tab with a flat surface is introduced as an intermediary element between the rack and shaft. This tab engages with a corresponding flat surface on the rack support, preventing relative rotation while allowing the manual wrench drive to operate the pinion and rack. The tab acts as a mediator that transmits the driving force without permitting unwanted rotational movement.
Solution Approach 2:
The flat surface on the tab and corresponding flat surface on the rack support create an asymmetric engagement that prevents rotation. Instead of a symmetric cylindrical connection that allows free rotation, the asymmetric flat surfaces engage at specific orientations, locking the rack to the shaft against rotational movement while maintaining the ability to transmit linear driving forces.
2Ease of operation
If the rack is allowed to rotate with the shaft, then manual wrench drive can move the valve to open position, but precise control of valve skirt position becomes difficult
Solution Approach 1:
The tab serves as a precision intermediary that ensures the rack moves only in the intended linear direction without rotational deviation. This mediator component guarantees that the manual wrench drive's rotational input is converted to precise linear motion of the rack, which in turn provides precise control of the valve skirt position.
Solution Approach 2:
The connection between the rack and shaft is segmented into distinct functional elements: the rack teeth for driving motion, the tab for preventing rotation, and the rack support for guiding movement. This segmentation allows each element to perform its specific function optimally, with the tab specifically dedicated to maintaining precise positional control by eliminating rotational degrees of freedom.
Data Source
AI summary
A valve skirt is connected to a shaft. The shaft extends in a rearward direction away from the skirt and has rack teeth at a location spaced away from the skirt. A tab is positioned between the skirt and the rack teeth, and has at least one flat surface. A rack support supports the rack for axial movement, and the rack support has a support ear that has a flat surface engaging the flat surface on the rack to prevent relative rotation of the rack when driven by a pinion gear. An air starter valve, a gas turbine engine and a method are also disclosed.