You can also visit a version of this mechanism with dwell in here.
The 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 a 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 caused by sliding friction and high contact pressures.
- Lesser percentage of the time spent at bottom dead center reducing blowdown time for two stroke engines.
The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed.