Four-Piston Scotch Yoke Actuator for High Torque in Compact Space
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Solution Overview
Problem
Scotch yoke actuators face limitations due to side loading effects on moving parts, which restrict their usefulness, especially in applications requiring high torque, and existing designs either compromise on size or torque output.
Innovation Solution
A four-piston Scotch yoke actuator design that achieves significantly higher torque without increasing size by utilizing a housing with equally spaced piston bores, a shaft with yokes and slots, and pistons with support members and guide rings, allowing for efficient conversion of linear to rotary motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a single-piston Scotch yoke actuator is used to achieve high torque, then torque output is improved, but device size increases significantly
Solution Approach 1:
The single-piston Scotch yoke actuator is segmented into four smaller pistons arranged at 90-degree intervals around a common shaft. Each piston operates in its own cylinder and contributes to the total torque output. This segmentation allows the actuator to achieve the same torque as a single-piston design while reducing the overall size and length of the actuator body.
Solution Approach 2:
The invention transitions from a single linear piston moving in one dimension to four pistons arranged radially in multiple dimensions around a central shaft. This spatial arrangement in three-dimensional space allows compact packaging while maintaining torque output, effectively utilizing volumetric space more efficiently than the conventional single-piston linear arrangement.
2Volume of moving object
If Scotch yoke design is used for compact dimensions, then device size is reduced, but side loading effects on moving parts increase
Solution Approach 1:
By dividing the load among four pistons instead of one, the side loading forces are distributed and reduced on each individual piston and the common shaft. Each piston handles a portion of the total load, reducing the harmful side loading effects that would occur in a single-piston design of equivalent torque output.
Solution Approach 2:
The four pistons are arranged at 90-degree intervals around the shaft, creating a balanced configuration where the side loading forces from opposing pistons counterbalance each other. This symmetric arrangement reduces net side loading on the shaft and bearings, mitigating the harmful effects while maintaining compact dimensions.
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 design nearly doubles the torque of rack-and-pinion actuators of similar size, matches the torque of single-piston Scotch yoke actuators, and is compact, providing a superior torque-to-size ratio while minimizing friction and wear through optimized piston and slot configurations.
Implementation Method 1
a linearly reciprocating push rod is coupled to the shaft by a lever arm or yoke that converts the linear movement of the rod to a rotary movement of the shaft
Implementation Method 2
a Scotch yoke actuator can be a double acting (DA) actuator in which fluid pressure moves the piston in both directions
Implementation Method 3
a spring return (SR) actuator in which fluid pressure moves the piston in one direction and a spring moves the piston in the opposite direction
Data Source
AI summary
A Scotch yoke actuator includes a housing formed with four piston bores spaced equally 90° from each other, a shaft with four yokes, each of the yokes having a slot, and four pistons including two pairs of 180° opposing pistons, one pair of the opposing pistons being orthogonal to the other pair of the opposing pistons. Each of the pistons is arranged for linear motion in one of the piston bores. Each of the pistons includes a piston rod which includes a piston pin which is slidable in the slot. Linear motion of the pistons in the piston bores causes rotation of the shaft.