303A: Gearing Principles

Question 1

A gear tooth can be divided into four distinctive quadrants. Identify the names of each of these quadrants.

Answer 1

Face
Flank
Toe
Heel

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Question 2

The gear pitch line is used to divide the following gear tooth areas:

Answer 2

Face and flank

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Question 3

When two gears are in mesh, a gap is formed between the tip of one gear tooth and the root in the opposite gear. This gap is called the:

Answer 3

Clearance. Helps maintain a lubrication film.

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Question 4

Explain why some angle drive gear sets may need to be timed.

Answer 4

To prolong service life and maintain the distinct wear pattern.

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Question 5

Gears may operate together as direct drive assemblies. Identify and explain two other types of gear configurations.

Answer 5

Reduction: Speed reduction, torque increase. Gear ratio of >1:1

Overdrive: Speed increase, torque reduction. Gear ratio of <1:1

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Question 6

If a simple gear set has a gear ratio of 4:1, explain which member is turning at 4 revolutions

Answer 6

• Reduction gear ratio
• Drive member is rotating 4x for each driven member rotation

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Question 7

Which of the following gear ratios would be a reduction gear ratio?

a) 0.10:1
b) 1.00:1
c) 10.00:1
d) 1.00:2

Answer 7

c) 10.00:1

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Question 8

When installed between a drive and a driven gear, an idler gear affects speed and torque changes between the two gears. (T/F)

Answer 8

False

It will only change the direction of rotation

Question 9

Explain the purpose of an idler gear

Answer 9

An Idler gear is used to change the direction of rotation in the output gear.

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Question 10

Name and explain the tooth design used on two types of external gears

Answer 10

• Straight cut spur gear: Teeth cut inline with the mounting shaft. Inexpensive, no axial loads, low strength
• Single Helical Gear: Teeth cut at angle to the mounting shaft. High strength, less noise, has axial loads.
• Double Helical Gear / Herringbone: Greater strength, opposing axial loads offset each other, expensive to manufacture.

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Question 11

Identify one common gearset where internal gears may be used

Answer 11

Planetary gear sets

Question 12

What is another name for a double helical gear?

Answer 12

Herringbone gears

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Question 13

Straight cut spur gears and helical gears both produce axial thrust loads during operation? (T/F)

Answer 13

False.
Straight cut gears do not produce axial loads.

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Question 14

Identify the 3 main components of a simple planetary gear set.

Answer 14

• Internal gear / ring gear
• Carrier / Planetary gears
• Sun gear

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Question 15

When a gear tooth has a larger and narrower end, the larger end is identified as the ____ , the middle as the ______ , and the narrower end is the _____.

Answer 15

Heel, Centre, and Toe

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Question 16

What does the term path-of-power mean in relation to gearing?

Answer 16

Tracing any power flow such as from the engine flywheel to the drive axles.

Used to determine which gears are in use delivering power.

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Question 17

When gears are used in mobile equipment, such as a differential crown and pinion, the drive side gear tooth has what shape?

Answer 17

Drive side is convex
Coast side is concave

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Question 18

What are three identifying gear measurements when viewed from the side?

Answer 18

• Root Circle
• Pitch Circle
• Outside Circle

Each is measured from one side of the gear, through the gear centre, to the opposite side of the gear.

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Question 19

In order to determine circular gear pitch, what must first be established?

Answer 19

The pitch circle, then the gear tooth centreline.

Circular gear pitch is the distance between the gear tooth centrelines along the path of the pitch circle.

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Question 20

What is the purpose of gear backlash?

Answer 20

To allow for expansion during operation and allow for lubrication.

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Question 21

If gear backlash is incorrect, what may need to be adjusted?

Answer 21

Gear mesh

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Question 22

Do hunting gear sets have to be timed?

Answer 22

No. Every pinion tooth will come into mesh with every crown gear tooth.

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Question 23

What are the advantages of straight cut spur gears?

Answer 23

• Inexpensive to manufacture
• No axial thrust loads

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Question 24

What are disadvantages of straight cut spur gears?

Answer 24

• Low strength
• Noisy

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Question 25

What is a major advantage of single helical gears?

Answer 25

• High strength due to multiple teeth in mesh at a time
• Reduced noise over straight cut gears

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Question 26

What gear set changes rotary motion into linear motion?

Answer 26

Rack and pinion

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Question 27

Hypoid angle gears and amboid gears have high load handling capability. What’s the difference between them?

Answer 27

Amboid Gears: Pinion gear is above centreline.

Hypoid Gears: Pinion gear is below the centerline.

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Question 28

What application could you see a strong but expensive worm and worm wheel gearset in?

Answer 28

Where high torque loads are handled.
Winch drives.

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Question 29

A planetary gear set needs a drive member, a driven member and a stationary or held member. What is another name for the stationary member?

Answer 29

The reactionary member

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Question 30

What are five various planetary gear set conditions?

Answer 30

• Direct drive: Any two locked together
• Reverse: Carrier held
• Reduction: Carrier driven
• Overdrive: Carrier driven
• Neutral: No members held

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