Presentation on theme: "Gear Drives Gear Drives"— Presentation transcript:
1 Gear Drives Gear Drives Rigid means of transmitting power between close shafts through the meshing action of their teeth.Smallest gear – Pinion.Can be driven or driving gearCan change both orientation and speed of rotary motionExamples – car differential, washing machine, others?Preferred over belts and chains when:Transmit power without slippageTiming devices (watches)Disadvantages - Higher costs and lubrication
2 Gear Drives Gears Characterized by: Number of Teeth (N) Pitch Diameter (D)Circular pitch (p)Diametral pitch (P)Pressure angle (ϕ)The diameter of the pitch circle. The pitch circle is the imaginary circle on which the contact point of the gears lie. Where power is transferred.
3 Gear Drives Circular Pitch (p) Diametral Pitch (P) Pressure Angle (ϕ) The length of the arc between corresponding points on adjacent teeth.Diametral Pitch (P)The ratio of the number of teeth per inch of pitch diameter.Pressure Angle (ϕ)The angle between the line of action and a line tangent to the pitch circleStandard angles - 20° & 14.5°Line of action – portion of the common tangent to the base cylinder along which contact between mating teeth occur.
4 Gear Drives 4 types of Gears: Spur Gear Helical Gear Most common Teeth cut parallel to axis of rotationGood for low to moderate speedsHelical GearTeeth not parallel to the shaftForm spiral around the bodyAllows smoother mating of the teethHigh thrust loadReduced bearing and shaft life
5 Gear Drives Bevel Gears Worm Gears Generally mounted on shafts 90° Good when a large speed reductionis needed.Worm can turn the gear but gearcannot turn the wormUsed to prevent rotation inone direction
6 Gear Drives Gear Alignment Speed and Gear Ratios Critical HorizontalVerticalParallelSpeed and Gear RatiosN(2)/N(1) = n(1)/n(2)N(1) = number of teeth of the driving gearN(2) = number of teeth of the driven gearn(1) = speed of the driving gear in RPMn(2) = speed of the driven gear in RPM
7 Gear DrivesCalculate the driven gear speed of a two gear drive having the following:Driving gear speed – 21 RPMNumber of teeth on the driving gear – 40Number of teeth on the driven gear – 20Driven gear speed - ???
8 Gear Drives Gear Trains Many gears to achieve desired speed between a driving component and driven component.Enclosed in a housing - Gearbox
9 Gear Drives Speed of the last shaft n(3) = [n(1) X N(1)]/N(3) n(1) = speed of the driving shaft (RPM)n(3) = speed of the last driven shaft (RPM)N(1) = number of teeth of the driving gearN(3) = number of teeth of the last driven gearGears installed in a series, speed of last shaft is only dependent on the:Speed of the first shaftTeeth ratio between the first and last gear
10 Gear DrivesCalculate the driven gear speed of the last shaft in a 3 Gear Train having the having the following:Driving gear speed – 21 RPMSecond gear speed – 30 RPMNumber of teeth on the driving gear N(1)– 40Number of teeth on the second gear N(2) – 20Number of teeth on the third gear N(3) – 10Driven gear speed of last shaft- ???