ME321 Kinematics and Dynamics of Machines Steve Lambert Mechanical Engineering, U of Waterloo 11/21/2018
Gears Spur Gears - Parallel shafts and ‘straight’ teeth 11/21/2018
Gears Example internal spur gear Example rack and pinion 11/21/2018
Helical Gears Helical gears are smoother and quieter than spur gears, but are more expensive, are not easily engaged, and they generate a thrust load 11/21/2018
Bevel Gears Straight bevel gears Skew bevel gears 11/21/2018
Hypoid and Worm Gears Hypoid gear Worm gear 11/21/2018
Fundamental Law of Gearing We require a constant velocity ratio. For this to be possible, the common normal of the contacting tooth flanks must always pass through the pitch point. 11/21/2018
Involute Action Imagine that the gears are replaced by two cylinders connected by a string This system will satisfy our fundamental law The path traced by Q will represent our tooth profile 11/21/2018
Involute Action These are equivalent. Path traced by point Q is an Involute. 11/21/2018
Gear Tooth Nomenclature 11/21/2018
Gear Nomenclature Pitch Circle Circular Pitch Addendum Dedendum Clearance Diametral Pitch: Circular Pitch: 11/21/2018
Standard Gears Diametral Pitch: 11/21/2018
Interacting Gears Centre Distance (r2 + r3) Contact Ratio Interference 11/21/2018
Contact Ratio Contact ratio is the average number of teeth in contact CR = length of line of action / base (circle) pitch CR = l / BP 11/21/2018
Contact Ratio CR = l / BP, where: Line of action: l = AC-AP + DB-DP 11/21/2018
Interference Interference occurs if point C falls outside point D - contact beyond involute profile occurs if O2C > O2D where: 11/21/2018