Gears-Force Transmission and Gear Train-paper

7/28/2019 Gears-Force Transmission and Gear Train-paper

1/19

Session #3Gears: Force Transmission &

Gear Trains

Dan Frey


2/19

Todays Agenda

Pass out second reading packet

Pass out loaner laptops

Introduce project teams

Gears Force Transmission

Gear Trains Survey


3/19

HW 1 Problem 1

A 17-tooth spur pinion paired with a 50 tooth gear has a diametral

pitch of 2 teeth/in and a 20o pressure angle. Make a drawing of

the gears showing one tooth on each gear (you may use a CADprogram or other techniques as appropriate, you may choose a

scale for your drawing as appropriate). Estimate the contact ratio.

Among other things, it is necessary that you be able to actually

draw the teeth on a pair of meshing gears. You should understand,

however, that you are not doing this for manufacturing or shop

purposes. Rather, we make drawings of gear teeth to obtain an

understanding of the problems involved in meshing of the mating

teeth. -Shigley and Mischke


4/19

Involute Profile

How it is constructed

Demo Properties

Conjugate action

Allows design ofwhole sets ofcompatible gears

Conjugate action notsensitive to center

distance variations


5/19

Concept Question

Are the teeth on a

matching rack andpinion set the same

shape?

1. Yes

2. No, never3. It depends on _____

Courtesy of OSHA.


6/19

Pressure Line

Where the teethcontact, the surface

normal defines apressure line

The force transmittedacts along this line

The pressure linealways includes thepoint of tangencybetween the pitch

circles With the involute

gear profile, thepressure line isconstant

Figure removed for copyright reasons.Source: Shigley and Mischke, Figure 13-17.

From Shigley and Mischke


7/19

Pressure Angle

The pressure lineacts at someangle to thetangent of thepitch circles

This angle can bechosen by thedesigner

It affects Separation forces

Tooth shape


From Shigley and Mischke


8/19

Gear

Terminology

Line of action &

pressure line &

generating lineare all synonymous

Source: Buchsbaum, Frank, Design and Application of

Small Standardized components Data Book 757Vol. 2,

Stock Drive Products, 1983.See Handbook of Gears. http://www.sdp-

si.com/D190/D190cat.htm (accessed 28 June 2006.)

Courtesy of Stock Drive Products/Sterling Instrument.


9/19

Concept Question

A pair of gears are mated. Oneis driven at a set torque, the

other is regulated at a set

speed. The gears are the onescircled. What is the ratio of the

separation forces and the total

force on the bearing?

1. > 0.5

Courtesy of W. M. Berg, Inc. Used with permission.


10/19

Discussion Questions

Are there any disadvantage

to a helical gear as comparedto a spur gear?

How can the disadvantages

be remedied? Is a helical gear set stronger

than a spur gear of the same

diameter, pitch, face width, &

material?

Image removed for Copyright reasons.


11/19

Simple Gear Trains

A simple gear train has

only one gear on eachshaft

How does thisarrangement behave?

1


12/19

Compound Gear Trains

A compound

gear train hasat least one

shaft with

multiple gears How does this

arrangement

behave?

Figure removed for copyright reasons.Source: Figure 9-29 in Norton, R. L. Design

of Machinery. 3rd edition. Burr Ridge, IL:McGraw-Hill, 2003.


13/19

Discussion Question

State a

relationshipone would

normally apply

in choosingradii for gears

3, 4, and 5

Figure removed for copyright reasons.Source: Figure 9-29 in Norton, R. L. Design

of Machinery. 3rd edition. Burr Ridge, IL:McGraw-Hill, 2003.


14/19

Manual Transmissions

Diagram of manual transmissioncomponents removed for copyright reasons.

If you find just two axles in a machine, does that meanthere are just two stages?


15/19

Discussion Questions How many stages in this device?

How do you suppose this number is chosen?

Are the reduction ratios typically all nearly the same in all

successive stages?10 teeth on pinion gear72 teeth

10 teeth

36 teeth

10 teeth

48 teeth

16 teeth42 teeth


16/19

Planetary Gear Trains

One or more of the gear axes are allowed to

rotate aka epicyclic

Used in

Power tools

Automatic transmissions

Gear boxes


17/19

Analysis of Planetary Gear Trains



18/19

Differentials

Allows shafts to move at different speeds

Applies same torque to both Slippage problem

What can be done?

See animations at http://auto.howstuffworks.com/differential3.htm


19/19

Next Steps

On Thurs 16 FEB (right here) next session

on gears

Finish HW#1

On Fri 17 FEB, the first lab in the lab

Gears-Force Transmission and Gear Train-paper

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