Scotch Yoke, Slotted Link, Withworth Return Mechanism
EXPERIMENT 4.1 – SCOTCH YOKE MECHANISM
BACKGROUND OF STUDY:
Pure simple harmonic motion is produced by the Scotch Yoke mechanism when driven by an eccentric or crank.
Its early application was on steam pumps but it is not suitable for high speeds due to the backlash in the scotch yoke. It is now mainly used in computing type applications where harmonic motion is required.
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 shape of the motion of the piston is a pure sine wave over time given a constant rotational speed.
This setup is most commonly used in control valve actuators in high pressure oil and gas pipelines.
Although not a common metalworking machine nowadays, crude shapers can use a Scotch yoke. Almost all those use a Whitworth linkage, which gives a slow speed forward cutting stroke and a faster return.
It has been used in various internal combustion engines, such as the Bourke engine, SyTech engine, and many hot air engines andsteam engines.
Figure 1.1 Piston water pump, with a scotch yoke connection to its flywheel
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Internal combustion engine uses
Under ideal engineering conditions, force is applied directly in the line of travel of the assembly. The sinusoidal motion, cosinusoidal velocity, and sinusoidal acceleration (assuming constant angular velocity) results 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 ofconnecting rod angle is mitigated. The longer the distance between the piston and the yoke, the less wear that occurs,
BACKGROUND OF STUDY:
Pure simple harmonic motion is produced by the Scotch Yoke mechanism when driven by an eccentric or crank.
Its early application was on steam pumps but it is not suitable for high speeds due to the backlash in the scotch yoke. It is now mainly used in computing type applications where harmonic motion is required.
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 shape of the motion of the piston is a pure sine wave over time given a constant rotational speed.
This setup is most commonly used in control valve actuators in high pressure oil and gas pipelines.
Although not a common metalworking machine nowadays, crude shapers can use a Scotch yoke. Almost all those use a Whitworth linkage, which gives a slow speed forward cutting stroke and a faster return.
It has been used in various internal combustion engines, such as the Bourke engine, SyTech engine, and many hot air engines andsteam engines.
Figure 1.1 Piston water pump, with a scotch yoke connection to its flywheel
-------------------------------------------------
Internal combustion engine uses
Under ideal engineering conditions, force is applied directly in the line of travel of the assembly. The sinusoidal motion, cosinusoidal velocity, and sinusoidal acceleration (assuming constant angular velocity) results 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 ofconnecting rod angle is mitigated. The longer the distance between the piston and the yoke, the less wear that occurs,