Scotch Yoke Mechanism

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Experiment 3 Statement: To Draw the Displacement, Velocity and acceleration Diagrams of Scotch Yoke. (Slotted Link Mechanism).

Apparatus: Scotch yoke mechanism

Diagram:

Theory: Scotch yoke mechanism: The Scotch yoke (also known as slotted link mechanism) is a reciprocating motion mechanism, converting the linear motion of a slider into rotational motion, or vice versa.

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Working principle: 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 location of the piston versus time is a sine wave of constant amplitude, and constant frequency given a constant rotational speed

Construction: It is constructed with iron bars. Here crank is made in some length and yoke is made using same material. It should be noted that minimum length of yoke should be twice of length of crank. The crank and yoke is connected with pin. Iron bars are welded to both sides of the yoke to get reciprocating motion. The yoke with iron bars is fixed on display board with the help of c clamp .

Advantage: Its advantage over crank shaft mechanism is that  it has lesser moving parts  smoother operation.

Disadvantages: Its disadvantages are:  Rapid wear of slot in the yolk caused by sliding friction and high contact pressures.  Increased hest loss during combustion due to extended dwell at top dead centre offset any constant volume combustion improvement in real engines.

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Applications:

 Control valve actuators: This setup is most commonly used in control valve actuators in high-pressure oil and gas pipelines. 

Crude shapers: Although not a common metalworking machine nowadays, crude shapers can use Scotch yokes.

Internal combustion engines:

Under ideal engineering conditions, force is applied directly in the line of travel of the assembly. The sinusoidal motion, co sinusoidal velocity, and sinusoidal acceleration (assuming constant angular velocity) result in smoother operation. The higher percentage of time spent at top dead center (dwell) improves theoretical engine efficiency of constant volume combustion cycles. It allows the elimination of joints typically served by a wrist pin, and near elimination of piston skirts and cylinder scuffing, as side loading of piston due to sine of connecting rod angle is mitigated. The longer the distance between the piston and the yoke, the less wear that occurs, but greater the inertia, making such increases in the piston rod length realistically only suitable for lower RPM (but higher torque) applications

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Observations And Calculations: Degrees

30

60

90

120

150

180

210

240

Displacem ent

3.2 5

16

33. 2

51

64

69

64.5 53

270

300

330

34.7 17.5 4.5

360 0

Conclusions:  The scotch yoke advantages and disadvantages are discussed .its motion characteristics are studied.  It is concluded that this mechanism is great choice can be used in direct injection engines like diesel engine to convert rotating motion into reciprocating motion because of fewer moving parts and smooth operation.