SCOTCH YOKE MECHANISM


Group Members:
(33)Komal Jogdand,  (34)Ameya Joshi,  (35)Ranbeer Kadam,  (36)Sonal Kadam,  (37)Viraj Kadlag 

Guide: Prof. Umesh Chavan

 

SCOTCH YOKE MECHANISM  (SYM)

fig 1. Scotch Yoke Mechanism

Introduction

This scotch yoke mechanism is  one of reciprocating motion mechanism, it should be convert an rotary motion into sliding of linear motion. When Piston part is been coupled together for  sliding of yoke with a slot, that will engage a pin at reciprocating part. by the means of crankshaft rotation the internal combustion engine is convert from rotary motion into linear motion. Where the Piston and connecting rod this both should be connected together. The Scotch Yoke Mechanism to be consider for more efficient because it spent high time in top dead center. 

Working principle of Scotch Yoke Mechanism(SYM)

It is a simple mechanism, in which rotary motion of pin convert into linear motion. The connected DC motor is been supplied by power to it, as soon as the shaft start the rotation moment, now the crank will rotate the pin slider inside of yoke part and also side by side it will move in forward direction.  yoke will be getting displacement moment at forward, when crank will be rotating in the clockwise direction. Maximum displacement of that yoke will depend on the length of Crank.

fig.2 

As the  crank is completed the clockwise Revolution at similar time only the Yoke sliding completely moved in forward direction, When this position take more time to start the return return stork. As the time will be going on, the crank will be again rotating continuously to come back in initial position of rotation.  


fig.3 Scotch yoke mechanism working gif 

So as the Yoke move in the  backward direction it will come back for the initial position. Therefore the crank has full Revolution to be completed, And also at the same time the Yoke will be completing its the forward and backward movement of Sliding. By the means of the full revolution of the Crank, the Yoke in it could be sliding through the equal of double length that of the Crank. By varying in the length of the crank the Yoke displacement can be controlled .

About Mechanism

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.

This mechanism is used for converting rotary motion into a reciprocating motion. The inversion is obtained by fixing either the link 1 or link 3. In Fig. link 1 is fixed.

In this mechanism, when the link 2 (which corresponds to crank) rotates about B as centre, the link 4 (which corresponds to a frame) reciprocates.

The fixed link 1 guides the frame.

fig. 4 

As,
number of links (n) = 4

Number of pairs (l) = 4

Degree of Freedom ( d.o.f ) = 3(n-1) – 2(l)

Therefore, d.o.f = 3(4-1) – 2(4)   =>  3(3)-8

∴  Degree of freedom = 1 

fig .5 




Applications:


fig.6:  piston water pump, with Scotch Yoke connection to its fly wheel

Above scotch yoke mechanism based this piston water pump lifts water from both side within minimum time by giving us high output, this types of pumps are widely used in agriculture sectors.

Considering another applications, it has been used in various internal combustion engines, such as the Bourke engine, SyTech engine, and many hot air engines and steam engines.

The term scotch yoke continues to be used when the slot in the yoke is shorter than the diameter of the circle made by the crank pin. For example, the side rods of a locomotive may have scotch yokes to permit vertical motion of intermediate driving axles.



Advantages of Scotch Yoke Mechanism

  • As there are few moving parts in it hence we get smoother operation.
  •  SYM  is used for perform of cutting of various materials, sliding and etc.
  • It is a directly convert method of rotary into Linear.
  • Higher Torque Output with small cylinder size
  • It spent high time in top dead center, so improve engine efficiency.

Disadvantages of Scotch Yoke Mechanism

  • Direct wear  of slot is produced due to sliding friction and high contact pressure in yoke.
  • List percentage of time spent in bottom  dead center, due to which it reduce the below time in two stroke engine. 
  • The Piston motion is a pure sine wave will occur overtime give a constant rotation speed. It requires proper guide way for reciprocating motion of arm
References:

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