Scotch yoke
From Wikipedia, the free encyclopedia
The Scotch yoke, also spelled Scotch Yoke and scotch yoke, is a mechanism for converting the linear motion of a slider into rotational motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part.
The advantages compared to a standard crankshaft and connecting rod setup are:
- High torque output with a small cylinder size.
- Fewer moving parts.
- Smoother operation.
- Higher percentage of the time spent at top-dead-center (dwell) improving engine efficiency.
- In an engine application, elimination of joint typically served by wrist pin, and near elimination of piston skirt and cylinder scuffing, as side loading of piston due to sine of connecting rod angle is eliminated.
The disadvantages are:
- Rapid wear of the slot in the yoke.
- Lower percentage of time at bottom-dead-center causing less time for evacuation of gasses from the cylinder.
The shape of the motion of the piston is a pure sine wave over time.
This setup is most commonly used in control valve actuators in high pressure oil and gas pipelines.
