Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Calculate velocity ratio and speed in drive systems.
• Describe the pros and cons of belt, chain, and gear drives.
• Identify different types of belts, chains and gears.
• Perform basic maintenance checks.
• Explain the importance of lubrication and alignment.

Lesson summary

This week, we delve into the crucial topic of power transmission systems. Understanding how power is transferred from one point to another is fundamental in mechanical engineering and is vital for the efficient operation of countless machines and devices we encounter daily. Whether it's the engine in a taxi transferring power to the wheels, the mechanism of a borehole pump providing water to a rural community, or the intricate workings of machinery in a manufacturing plant, power transmission systems are indispensable. These systems use belts, chains, and gears, each possessing unique characteristics and applications.

Lesson notes

2.1 Belt Drives Belt drives use flexible belts to transmit power between shafts. They are relatively inexpensive, quiet, and can absorb shock, making them suitable for a wide range of applications.

Types of Belts: V-belts: The most common type, offering good grip and power transmission. They are trapezoidal in cross-section and fit into matching grooves on pulleys.

Flat belts: Older design, less efficient than V-belts but can operate at high speeds. They rely on friction for power transmission.

Synchronous belts (Timing Belts): Have teeth that mesh with corresponding teeth on the pulleys, providing positive drive and preventing slippage. Used where precise timing is essential, like in engine camshafts.

Ribbed belts (Poly-V belts): Combine the advantages of flat and V-belts, offering high power transmission capacity and flexibility.

Velocity Ratio (VR) / Speed Ratio (SR): The velocity ratio is the ratio of the speed of the driver pulley to the speed of the driven pulley. VR = Speed of Driver (N 1 ) / Speed of Driven (N 2 ) = Diameter of Driven (D 2 ) / Diameter of Driver (D 1 ) N represents the rotational speed (usually in revolutions per minute - RPM), and D represents the diameter of the pulley.