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IDIS 303 > Chapter 4 - Gears > Flashcards

Chapter 4 - Gears Flashcards

1
Q

Types of gears

A 
Spur
Helical
Bevel
Worm
Hypoid
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2
Q

Gears

A

Earliest form of power transmission.
Class one lever.
Generally speed reducers and torque increasers.
Transmit torque and speed to create motion by direct contact.

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3
Q

Driver Gear

A

Transmits the torque.

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4
Q

Terminology of a gear

A 
Pressure angle
Face width
Addendum
Dedendum
Circular pitch
Pitch circle
Pitch diameter
Outside diameter
Root diameter
Clearance
Whole depth
Center distance
Circular tooth thickness
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5
Q

Pressure angle

A

Angle between normal of the tooth and the tangent of the gear.

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6
Q

Face width

A

Length of a tooth running along the gear axis

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7
Q

Addendum

A

Difference between outside diameter and pitch circle.

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8
Q

Dedendum

A

Difference between pitch circle and root diameter.

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9
Q

Pitch Cylinder

A

Point of contact on tooth when gears mesh together and the tangent of each gear creates a straight line.

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10
Q

Pitch Circle

A

Circle around the gear that corresponds with all pitch cylinders.

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11
Q

Pitch Diameter

A

Diameter of the pitch circle.

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12
Q

Pinion

A

Smaller gear and usually the driver gear.

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13
Q

Clearance

A

Difference between addendum and dedendum of a tooth.

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14
Q

Full Depth of Teeth

A

Total depth of the tooth space.

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15
Q

Working depth of teeth

A

The max depth that a tooth penetrates into the tooth space of the mating gear.

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16
Q

Working Depth

A

Sum of addendums of two gears.

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17
Q

Space Width

A

Width of the space between teeth along the pitch circle.

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18
Q

Tooth Thickness

A

Thickness of a tooth along the pitch circle.

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19
Q

Backlash

A

Difference between the space width and tooth thickness.

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20
Q

Top Land

A

The surface of the top of the tooth.

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21
Q

Bottom Land

A

Surface between bottoms of teeth excluding fillets.

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22
Q

Flank

A

Surface between pitch circle and the bottomland including fillet.

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23
Q

Fillet

A

Curved portion of the tooth flank at the root circle.

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24
Q

Circular Pitch

A

Distance along the pitch circle from one point on a tooth the the corresponding spot on the next tooth.

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25
Q

Diametrical Pitch or Module

A

Number of teeth per unit length of the pitch circle diameter in inches.
Module is same but in mm.

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25
Q

Module

A

Ratio of pitch diameter to the number of teeth in mm.

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26
Q 
1 3/4 DP=
2 DP=
2 1/2=
3=
3 1/2=
4=
5=
6=
7=
8=
10=
12=
14=
16=
18=
20=
A

1.7952” Circular Pitch
1.5708”
1.2566”
1.0472”
.8976”
.7854”
.6283”
.5236”
.4488”
.3927”
.3142”
.2618”
.2214”
.1963”
.1745”
.1571”

26
Q

Idler

A

Makes the shaft rotation of one gear to another in the same direction. Has no effect on torque or speed transmitted.

27
Q

Open Gear Types by Shafts:

A

Parallel Shafts
Intersecting Shafts
Skew Shafts

27
Q

Parallel Shaft Gears:

A 
Spur
Helical
Double Helical
Internal
Rack and Pinion
27
Q

Intersecting Shaft Gears:

A

Straight Bevel Gears
Spiral Bevel Gears
Zerol Bevel Gears
Skew Tooth Gears

27
Q

Skew Shaft Gears:

A

Crossed-helical Gears
Worm gears
Hypoid Gears

28
Q

Spur Gear

A

Basic form of gear.
Straight teeth parallel to axes and not subject to axial thrust.
Moderate Speed, low cost, low maintenance.
Most widely used gear type.

29
Q

Spur Gear Coarse Type:

A

1-19 Diametrical Pitch

30
Q

Spur Gear Fine type:

A

20+ Diametrical Pitch

31
Q

Spur Gear Standard Teeth types:

A

14 1/2-deg coarse pitch
20-deg coarse pitch
20-deg fine pitch
25-deg coarse pitch

32
Q

Helical Gears

A 
Teeth are at an angle.
Produce thrust load on both shafts.
Carry more load, less vibration, higher speeds and quieter.
Mating Gears have same helix angle.
RH & LH to mesh.
33
Q

Double Helical Gears

A

Pair of Helical gears secured together.
Cancels axial or thrust force.
Higher Speeds, less noise, less vibration.

34
Q

Herringbone Gear

A

A Double Helical Gear with no groove in-between.

35
Q

Internal Gear

A

Can be spur or helical type.
Advantage is space constrain.
Same direction of rotation.

36
Q

Spur Rack and Pinion

A

Indefinite diameter.
The rack is a straight rectangular bar with teeth.
Converts rotary motion into linear motion or vise versa.

37
Q

Bevel Gears

A

Axes usually at 90 deg but sometimes different.

Produce thrust load on both shafts.

38
Q

Four types of bevel Gears:

A 
Straight
Spiral
Zerol
Skew
Hypoid-non intersecting shafts
39
Q

Straight Bevel Gear

A

Simplest and most common bevel gear.
Teeth (if extended) come to a common point.
Outermost point of teeth is the thickest.
Don’t need to be the same size.

40
Q

Spiral Bevel Gear

A

Teeth are inclined and at an angle to the face of the bevel.
Have overlapping teeth that result in less noise.
Axial thrust exists.
Used for a differential in an automobile.

41
Q

Zerol Bevel Gear

A

Have curved teeth but have zero-degree spiral angles.))))

High contact ratios, less noise and vibration, high efficiency (>97%).

42
Q

Skew Tooth Gear

A

Gears are spiraled but teeth are not curved, teeth are cut at an angle to the centerline.
Used for large diameters (>30” pitch diameters).

43
Q

Crossed-Helical Gear

A

Shafts are at an angle and don’t intersect.

Light loads, sliding action, must be lubed.

44
Q

Worm Gear

A

Most popular gear configuration.
Consist of threaded worm and a worm wheel.
Worm slides along wheel teeth, and takes several rotations for one rotation of wheel.
Worm always drives the wheel. CW or CCW.
Low efficiency (50-90%)..

45
Q

Types of Worm Gears:

A

Cylindrical worm meshing with a helical gear.
Single-enveloping gear-wheel has curved teeth to partially wrap.
Double-enveloping gear-worm and wheel are curved to wrap each other.

46
Q

Hypoid Gear

A

Similar to spiral bevel gears but the shafts don’t intersect.

47
Q

Gear Trains

A

Multiple gears form together to make a gear train.

48
Q

Gear Train Types:

A 
Simple Gear Trains
Compound Gear Trains
Planetary Gear Trains
Epicyclic Gear Trains
Harmonic Gear Trains
49
Q

Simple Gear Trains

A

All gears lie in the same planes.

50
Q

Compound Gear Trains

A

Multiple gears on the same shaft.

51
Q

Planetary Gear Trains

A

Sun Gear is the main driving gear. Planet gears around mounted around it.

52
Q

Epicyclic Gear Trains

A

Direct competitor of planetary.

Very high gear ratios (100:1).

53
Q

Harmonic Gear Trains

A

Gear ratios in order of 1000:1.

Rollars force flexible gear to contact the ring gear on opposite sides.

54
Q

Speed Reducers Types:

A

Worm-Gear Speed Reducers
Helical-Gear Speed Reducers
Planetary Speed Reducers

55
Q

Worm-Gear Speed Reducers

A

Low cost, low efficiency, very quiet.
Up to 100:1.
Single-reduction, Double-reduction(60-3600:1), Triple-reduction(-180,000:1).

56
Q

Helical-Gear Speed Reducers

A

High efficiency,
1,2,3,or4 set of gears.
Total reduction=multiple of each reduction.

57
Q

Planetary Speed Reducers Types:

A

Single-Stage or Simple Planetary Reducers.

Differential Planetary Reducers.

58
Q

Single-Stage or Simple Planetary Reducers

A

Consist of sun gear that drives three planetary gears.
Planet carrier is surrounded by planet gears.
Ratio=1+(Nring/Nsun) N=# teeth

59
Q

Differential Planetary Reducers

A

Construction is same as simple planetary reducer except planetary gears are supported by a free-floating planet carrier which is free to rotate about the sun gear.

60
Q

Factors in Reducer Selection

A 
Load Ratings
Service Factors
Horse Power
Torque
Gear Ratio
Overhang and bending loads

IDIS 303 (8 decks)

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