Introduction Of Gears Classification Of Gears According To Toothed Wheels Classification Of Gears Planetary (OR Epicyclic) Gears Nomenclature Of Gear TeethAdvantages & Disadvantages Gear Box Design
Gears are used to transmit motion from one shaft to another or between shaft and a slide. This is achieved by successfully engaging teeth. Gears used no intermediate links or connector and transmit the motion by direct contact. The surface of two bodies make a tangential contact. The two bodies have either a rolling or a sliding motion along the tangent at the point of contact.
To avoid axial thrust, two helical gears of opposite hand can be mounted side by side, to cancel resulting thrust forces Herringbone gears are mostly used on heavy machinery. Axial Thrust is a force that is generated in an axial direction which is along the shaft.
Fig.:-Lathe carriage drive mechanism showing rack and pinion arrangement.
Fig.:- Helical tooth rack and pinion Fig.:- Spur tooth rack and pinion
Gears whose centers can move. Used to achieve large speed reductions in compact space. Can achieve different reduction ratios by holding different combinations of gears fixed. Used in automatic transmissions of cars.
Planet Carrier Input shaft Sun gear Ring gear Components Of A Planetary Gear
They have higher gear ratios. They are popular for automatic transmissions in automobiles. They are also used in bicycles for controlling power of pedaling automatically or manually. They are also used for power train between internal combustion engine and an electric motor.
Pitch circle gear diam. Fillet radius Clearance Base Circle
1. Pitch Circle : - It is an imaginary circle which by pure rolling action, would give the same motion as the actual gear. 2. Pitch Circle Diameter : - It is the diameter of the pitch circle. 3. Pitch Point : - It is a common point of contact between two pitch circles. 4. Pitch surface : - The surface of the imaginary rolling cylinder (cone, etc.) that the toothed gear may be considered to replace. 5. Addendum circle : - A circle bounding the ends of the teeth, in a right section of the gear. 6. Root or Deddendum circle : - The circle bounding the spaces between the teeth, in a right section of the gear. 7. Addendum : - The radial distance between the pitch circle and the addendum circle. 8. Deddendum : - The radial distance between the pitch circle and the root circle.
11. Flank of a tooth : - The part of the tooth surface lying inside the pitch surface. 12. Circular thickness ( also called the tooth thickness ) :- The thickness of the tooth measured on the pitch circle. It is the length of an arc and not the length of a straight line. 13. Tooth space : - The distance between adjacent teeth measured on the pitch circle. 14. Backlash : - The difference between the circle thickness of one gear and the tooth space of the mating gear. Backlash = Space width – Tooth thickness 15. Circular pitch (Pc) : - The width of a tooth and a space, measured on the pitch circle or it is the distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth. 16. Diametral pitch (Pd) : - The number of teeth of a gear per inch of its pitch diameter. A toothed gear must have an integral number of teeth. The circular pitch, therefore, equals the pitch circumference divided by the number of teeth. The diametral pitch is, by definition, the number of teeth divided by the pitch diameter. 17. Module (m) : - Pitch diameter divided by number of teeth. The pitch diameter is usually specified in inches or millimetres; in the former case the module is the inverse of diametral pitch.
Types Features and Precision Rating Applications Comments Regarding Precision SpurParallel Shafting. High speeds and loads highest efficiency Precision Rating is excellent. Applicable to all types of trains and a wide range of velocity ratios. Simplest tooth elements offering maximum precision. First choice, recommended for all the gear meshes, except where very high speeds and loads or special features of other types, such as right angle drive, cannot be avoided. Helical Parallel Shafting. Very high speeds and loads. Efficiency slightly less than spur mesh. Precision Rating is good. Most applicable to high speeds and loads; also used whenever spurs are used. Equivalent quality to spurs, except for complication of helix angle. Recommended for all high-speed and high-load meshes. Axial thrust component must be accommodated.
Bevel Intersecting shafts, High speeds, High loads. Precision Rating is fair to good. Suitable for 1:1 and higher velocity ratios and for right- angle meshes (and other angles) Good choice for right angle drive, particularly low ratios. However complicated both form and fabrication limits achievement of precision. Should be located at one of the less critical meshes of the train. Worm & Worm Right-angle skew shafts, High velocity ratio, High speeds and loads, Low efficiency, Most designs nonreversible. Precision rating is fair to good. High velocity ratio Angular meshes High loads. Worm can be made to high precision, but worm gear has inherent limitations. To be considered for average precision meshes, but can be of high precision with care. Best choice for combination high velocity ratio and right-angle drive.
Types Features and Precision Rating ApplicationsComments Regarding Precision Specials - Face, Spiroid, Helicon, Beveloid. Intersecting and skew shafts. Modest speeds and loads. Precision Rating is fair to good Special cases To be avoided as precision meshes. Significant non- conjugate action with departure from nominal center distance and shaft angles. Fabrication needs special equipment and inspection is limited.