types of gears
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Mechanical Engineering Dept. 1
Gears
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Mechanical Engineering Dept. 2
Applications of Gears
• Control gears – long life, low noise, precision gears
• Aerospace gears – light weight, moderate to high load
• Power transmission – long life, high load and speed
• Appliance gears – long life, low noise & cost, low to moderate load
• Toys and Small Mechanisms – small, low load, low cost
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Mechanical Engineering Dept. 3
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Mechanical Engineering Dept. 4
Types of Gears
Spur gears – tooth profile is parallel to the axis of rotation, transmits motion between parallel shafts.
Pinion (small gear)
Gear (large gear)
Internal gears
– teeth are inclined to the axis of rotation, the angle provides more gradual engagement of the teeth during meshing, transmits motion between parallel shafts.
Helical gears
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Mechanical Engineering Dept. 5
Types of Gears
Bevel gears – teeth are formed on a conical surface, used to transfer motion between non-parallel and intersecting shafts.
Straight bevel gear
Spiral bevel gear
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Mechanical Engineering Dept. 6
Types of Gears
Worm gear sets – consists of a helical gear and a power screw (worm), used to transfer motion between non-parallel and non-intersecting shafts.
Rack and Pinion sets – a special case of spur gears with the gear having an infinitely large diameter, the teeth are laid flat.
Rack
Pinion
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Types of gears
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Mechanical Engineering Dept. 8
Nomenclature of Spur Gear Teeth
= (tooth spacing)driven gear – (tooth thickness)driver , measured
on the pitch circle.
Backlash
Pitch circle gear diam.
Fillet radiusClearance
Base Circle
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Mechanical Engineering Dept. 9
Useful Relations
P = N / d
P = diametral pitch, teeth per inch
N = number of teeth
d = pitch diameter (gear diameter)
m (module, mm) = d / N
Metric system
p (circular pitch) = πd / N
Pp = π
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Mechanical Engineering Dept. 10
Standard Tooth SpecificationsPressure angle
Two mating gears must have the same diametral pitch, P, and pressure angle, φ.
Pitch line
Line of centers
Line of action
Base circle
Base circle
Pitch circle
Pitch circle
Pressure angle φ
Standard pressure angles, 14.5o (old), 20o, and 25o
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Template for teeth of standard gears
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Standard Gear Specifications
Parameter Coarse pitch (pd=N/d<20)
Fine pitch (pd=N/d>20)
Pressure angle, 200 or 250 (not common) 200
Addendum, a 1/pd 1/pd
Dedendum, b 1.25/pd 1.25/pd
Working depth 2.00/pd 2.00/pd
Whole depth 2.25/pd 2.2/pd+0.002
Circular tooth thickness 1.571/pd (circular pitch/2) 1.571/pd
Fillet radius 0.30/pd Not standardized
Clearance 0.25/pd 0.25/pd+0.002
Minimum width at top land
0.25/pd Not standardized
Circular pitch /pd /pd
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Mechanical Engineering Dept. 13
Kinematics of Gear Trains
Conventional gear trains
ω3
ω2=
N2
N3
ω3 ω4= , ω5
ω4=
N4
N5
,
mV = e = train value
Speed ratio
ω5
ω2=
outputinput=
Reverted gear train – output shaft is concentric with the input shaft. Center distances of the stages must be equal.
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Planetary (or Epicyclic) Gears
• 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
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Planetary gear
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Planet
Carrier
Input shaft
Sun gearRing gear
Components of a planetary gear
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A variant of a planetary gear
Carrier
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EngineGear
Propeller, operates at about 100 RPM
Output flange
Engine operates at about 400 RPM
Connecting the main engine to the propeller through a reduction gear
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Gear box
Synchronizers
Stick shift
The gear box is in first gear, second gear
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Planetary gears
Planetary gears in automotive transmission