A Comprehensive Introduction to Gears and Their Types: Fundamental Concepts, Classifications, Working Principles, and Applications for B.Tech 4th Semester Mechanical Engineering Students under Jharkhand University of Technology Curriculum

This presentation belongs to the B.Tech 4th Semester Mechanical Engineering course under the curriculum of Jharkhand University of Technology (JUT). The primary objective of this presentation is to provide a clear and fundamental understanding of gears and their various types.

Gears are one of the most essential elements in mechanical systems, widely used for the transmission of power and motion between rotating shafts. They play a vital role in machines, automobiles, industrial equipment, and many other mechanical applications. By using gears, engineers can change the direction of motion, increase or decrease speed, and alter torque according to the functional requirement of a system.

In this presentation, the focus will be on the basic concepts of gears, their classification, and the working principles behind different types. The types of gears, such as spur gears, helical gears, bevel gears, and worm gears, will be discussed along with their applications and advantages. The content is designed to give students an introductory but comprehensive view of gear mechanisms, which form the foundation for advanced topics in machine design and power transmission.

Through this study, students will develop a strong base for understanding the practical applications of gears in real engineering problems.

1. KINEMATICS OF MACHINES GEARS Created and Presented by Dr. Chandan Prasad Assistant Professor Netaji Subhas University, Jamshedpur, Jharkhand

2. G EAR A gear is a rotating machine element with cut teeth that mesh with another toothed part to transmit torque. Gears are mainly used to transfer motion and power between machine parts. They are preferred for transmitting power where slip is not desirable.

3. Functions of Gears ✅ To transmit rotary motion from one shaft to another. ✅ To change speed (increase or decrease) between the driving and driven shafts. ✅ To change the direction of rotation. ✅ To increase mechanical advantage. ✅ To transmit motion without slip.

4. Advantages of Gear Drives ✔ Constant velocity ratio. ✔ Compact design, suitable for short distances. ✔ High efficiency (up to 98%). ✔ Long service life with proper lubrication. ✔ Suitable for high-load and high-speed applications. Disadvantages of Gear Drives ✖ Requires precise manufacturing and assembly. ✖ High initial cost. ✖ Requires lubrication and maintenance. ✖ Not suitable for very long-distance power transmission.

5. Classification of Gears Gears can be classified based on the relative position of their shafts: On both axis are parallel. Spur Gear : Straight teeth parallel to the shaft; most common type. Pure rolling motion can be transmitted between two cylindrical surfaces in contact. Teeth are straight and parallel to the axis of rotation. Transmit motion between parallel shafts. No axial thrust generated. Impact stress is generated. Used in clocks, washing machines, and gearboxes.

6. Helical Gear : Teeth are inclined to the axis; smoother and quieter operation. Teeth are straight but inclined to the axis of rotation. Teeth cut at an angle to the face of the gear. Transmit motion between parallel shafts. Generates axial thrust. Smooth and quiet operation; used in automotive transmissions.

7. b) Axes are not parallel, but Intersecting Shaft Gears Bevel Gear : Conical-shaped gears; used when shafts intersect, usually at 90°. Spiral Bevel Gear : Like bevel gears but with curved teeth for smooth engagement. Two axis are mutually perpendicular than the bevel gear is known as mitre gears. Bevel Gear Pure rolling motion can be transmitted between two conical surfaces in contact. Conical-shaped gears. Transmit motion between intersecting shafts (commonly at 90°). Available as straight bevel, spiral bevel, and zerol bevel gears. Used in differential drives, hand drills, etc.

8. c) Non-Parallel, Non-Intersecting Shaft Gears Hypoid Gear : Similar to spiral bevel but shafts do not intersect; used in car differentials. Widely used in automobile differentials , especially in rear-wheel-drive vehicles. Industrial machinery where high torque and quiet operation are required. Heavy-duty trucks and buses. Aerospace mechanisms with space constraints and high-load requirements.

9. A screw (worm) meshes with a worm wheel; provides high reduction ratios. Worm and Worm Wheel Worm resembles a screw; meshes with a worm wheel (gear). Provides large speed reductions in compact space. A self-locking feature is possible. Used in elevators, conveyor systems. Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater. Many worm gears have an interesting property that no other gear set has the worm can easily turn the gear, but the gear cannot turn the worm. Worm gears are used widely in material handling and transportation machinery, machine tools, automobiles etc. Worm Gear

10. Rack and Pinion The Rack and Pinion is a type of gear mechanism used to convert rotary motion into linear motion , or vice versa. It consists of two main components: ✅ Rack – A straight or flat toothed bar. ✅ Pinion – A circular gear that meshes with the rack. As the pinion rotates, the rack moves in a straight line, making this system ideal for mechanisms that require precise linear motion controlled by rotary input. ✔ Steering Mechanism of Automobiles – Most cars use rack and pinion systems for precise and responsive steering control. ✔ Machine Tools – Used for linear positioning of components. ✔ Railway Systems – Used in rack railways for trains climbing steep gradients. ✔ Lifting Systems – Some elevators and hoists use rack and pinion drives. ✔ Industrial Automation – For controlled linear motion in various machines.

11. Gear Terminology

12. Gear Terminology Pitch Circle An imaginary circle that rolls without slipping with the pitch circle of a mating gear. All gear calculations are based on this circle. The size of the gear is specified by the Pitch Circle Diameter (PCD). 2. Addendum The radial distance between the pitch circle and the top of the teeth (outermost point). 3. Dedendum The radial distance between the pitch circle and the bottom of the tooth space (root of the gear). 4. Tooth Thickness The thickness of the gear tooth measured along the pitch circle. 5. Clearance The distance between the root of one gear tooth and the top of the mating gear tooth when gears are fully engaged. 6. Module (m) A measure of the size of gear teeth. Defined as the ratio of pitch circle diameter to the number of teeth. Formula: m = D / T Where: m = Module (mm); D = Pitch circle diameter (mm); T = Number of teeth 7. Pressure Angle (Φ) The angle between the line of action (line along which force is transmitted) and the tangent to the pitch circle. Standard values:14.5° - 20°

13. 8. Pitch a) Circular Pitch (Pc) The distance from one point on a tooth to the corresponding point on the adjacent tooth, measured along the pitch circle. Formula: Pc = π × m b) Diametral Pitch (Pd) The number of teeth per unit of pitch circle diameter. Formula: Pd = T / D 9. Face Width The width of the gear tooth measured parallel to the axis of rotation. 10. Backlash The slight clearance or play between meshing teeth. Necessary to compensate for manufacturing inaccuracies, thermal expansion, and to prevent jamming. 11. Addendum Circle The circle passing through the tip of the teeth. Lies above the pitch circle by the amount of the addendum. 12. Base Circle The circle from which the involute profile of the gear teeth is generated. Importance: In involute gears, tooth profiles are defined based on the base circle. 13. Line of Action The path along which the force is transmitted between mating teeth. Lies tangent to both base circles.