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.

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30 Apr 2013

Everything about scotchyoke mechanism....i want to know

Johann Wegmann Morovic
04 Aug 2013

Dear Gentlemen,Thankyou very much for this article.I´´ve been Reliability RCM,CAD/FEA and Simulation events user.I am astonished with Bourke cycle engine,the best engine never known,with a Scotch Yoke drive in center.20.000 rpm limit.
RCM has resources for enlarging life span,probably ductile cast iron ferrochrome,spheroidal grapfite, or MM´c composite.
My concern is , I am shamed,I am retired and never saw the tecnique to control de direction of rotation.My other concern is
In comparison,between a rhombic drive and scotch yoke ,at the same reliability service,which is the cheapest?Thanks

Johann Wegmann Morovic
11 Aug 2013

Dear Sirs,
1.-¿Cómo controlo el sentido de rotación en Stirling Motores?CW o CCW?
2.-¿Cual es mejor:Rómbico,Yunque Escosés,o slider-Crank,corredera ,cruzeta y biela?Confiabilidad, Tiempo entre Mantenciones. Gracias Johann wegmann

johann wegmann
07 Oct 2013

I am working in Alpha Stirling Engine,reciprocating and opposed pistons,double or simple action,opposed burners, Nichrome,Infrared or Radioisotops generator to replace gas burners definitivelle savibf 20% termal efficiency,alphas need to change kinematics configuration,it doesnt fit with PV diagram,the use of refrigeating expansion valve will dramatically lower cold cylinder lowest temp,the concept of adiabatic engine i developed in 1972, to day is ceramic coated possible and ringless pstons ceramic coated is adiabatic wall,I wiil increase Cmpression Ratio to 10:1,Temp.Ratio will increase.water ref if ceramic doesnt work, is an old usage to keep the liners within melting point.Please dwells both sides is interesting, I´ll change Bourke dnamics for a symetric piston motion,2 power strokes same time,Bye.Thanks.No one drun displacer is suitable to wwwithstand concentrated strength on shell elements,only vertical can run centerd,is for models,World wide Science,I guess, I read the champions design selection,first alpha in-line, secod 90 alpha,probably V configuration.Throtling valve and ceramic will make this engies take off.And my inside cylinders alectric,Infrared or Cerium based radioisotopes, will become Wegmann-Stirling engine.Best Regards.Johann

01 Feb 2014

""this mechanism is to be high torque to achived so many machines to be used ""

15 Apr 2014

i want to know the full dimensions of the skotchyoke mechanism

Keerthivasan Jayakumar
28 Apr 2014

Thank u for sharing scotch mechanism an it is really useful in my further projects

10 Nov 2014

thanks for sharing this mechanism on it .it is very nice to understood ,

19 Jun 2015

Do you have any calculations or spread sheets to shw velocities and torques acting on the slot

06 Nov 2015

can u pls explain why the rotation occurs always in the same direction. as far as i can see there is no reason for a random direction change at the end of the stroke. tks for explaining more.

06 Nov 2015

Dear Troll,
Thank you for your visit to my channel.
You are right, it can rotate in either way.

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