Upload
dr-nouby-mahdy-ghazaly
View
245
Download
0
Embed Size (px)
Citation preview
8/12/2019 Theory of Machines -Lecture1
1/30
ENM 222
Theory of MachinesLecture 1: Gears
Dr. Nouby M. Ghazaly
Mechanical Engineering Dept., Faculty of Engineering,
South Valley University,
Qena-83523, Egypt.
Email: [email protected]
8/12/2019 Theory of Machines -Lecture1
2/30
ENM 222 : -
- - - - - - -
- - - - . - : - -
) -( - - - -
- V - -.
3/8/2014 Dr. Nouby M. Ghazaly 2
8/12/2019 Theory of Machines -Lecture1
3/30
Outline of Presentation
Power transmission Definition of Gear Why Using Gears Types of gears Advantages &Disadvantage Applications of gears
3/8/2014 Dr. Nouby M. Ghazaly 3
8/12/2019 Theory of Machines -Lecture1
4/30
GEARS
Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work
A gear is a component within a transmission device thattransmits rotational force to another gear or device
3/8/2014 Dr. Nouby M. Ghazaly 4
8/12/2019 Theory of Machines -Lecture1
5/30
Gears
DEFINITION OF GEARSA gear is a wheel with teeth on its outer edge.The teeth of one gear mesh (or engage) with the teethof another.
Gears meshing or engaged
3/8/2014 Dr. Nouby M. Ghazaly 5
8/12/2019 Theory of Machines -Lecture1
6/30
Gears Motion
Driver and Driven Two meshed gears always rotate in opposite directions.
Driver gearDriven gear
3/8/2014 Dr. Nouby M. Ghazaly 6
8/12/2019 Theory of Machines -Lecture1
7/30
Gears
Idler gear
Driver
Driven
Idler gear
3/8/2014 Dr. Nouby M. Ghazaly 7
8/12/2019 Theory of Machines -Lecture1
8/30
Why Use Gears?
Reduce speed Increase torque
Move power from one point to another Change direction of power Split power
Generally this functionality is accomplished by manygears mounted in a gear box!
3/8/2014 Dr. Nouby M. Ghazaly 8
8/12/2019 Theory of Machines -Lecture1
9/30
TYPES OF GEARS Gears are classified according to the shape of the tooth pair and
disposition into spur, helical, double helical, straight bevel, spiralbevel and hypoid bevel, worm and spiral gears, Rack and pin Gears
3/8/2014 Dr. Nouby M. Ghazaly 9
8/12/2019 Theory of Machines -Lecture1
10/30
SPUR GEAR
Spur gears tooth profile is parallel to the axis ofrotation, transmits motion between parallelshafts.
Pinion (small gear)
Gear (large gear)
Internal gears
3/8/2014 Dr. Nouby M. Ghazaly 1. 10
8/12/2019 Theory of Machines -Lecture1
11/30
SPUR GEAR
Teeth is parallel to axis of rotation Transmit power from one shaft to
another parallel shaft Used in Electric screwdriver,
clock, gearbox, washing machineand many mechanical machine
3/8/2014 Dr. Nouby M. Ghazaly 11
8/12/2019 Theory of Machines -Lecture1
12/30
Advantages &Disadvantagesof Spur Gears
Advantages Cost Ease of manufacture Availability
Disadvantages Only works with mating gear
Axis of each gear must beparallel
3/8/2014 Dr. Nouby M. Ghazaly 12
8/12/2019 Theory of Machines -Lecture1
13/30
Helical Gear
3/8/2014 Dr. Nouby M. Ghazaly 13
Teeth are inclined to the axis of rotation, the angle provides moregradual engagement of the teeth during meshing.
Teeth angle to the gear axis (usually 10
to 45
) called helix angle.
It can be mounted on perpendicular shafts, adjusting the rotationangle by 90 degrees
8/12/2019 Theory of Machines -Lecture1
14/30
Helical Gears
Advantages Smooth and quiet due to gradual tooth engagements (spur gears
whine at high speed due to impact). Helical gears good up tospeeds in excess of 5,000 ft/min
More tooth engagement allows for greater power transmission forgiven gear size. Can withstand the largest capacity at 30,000 hp.
Parallel to perpendicular shaft arrangement.
Disadvantage More expensive Resulting axial thrust component
3/8/2014 Dr. Nouby M. Ghazaly 14
8/12/2019 Theory of Machines -Lecture1
15/30
8/12/2019 Theory of Machines -Lecture1
16/30
Bevel Gears
Bevel gears are used to transfer drivethrough an angle of 90 o.
Teeth are formed on conical surfaces,
the teeth could be straight or spiral.
3/8/2014 Dr. Nouby M. Ghazaly 16
8/12/2019 Theory of Machines -Lecture1
17/30
Bevel gears
Bevel gears are useful when the direction of a shaft'srotation needs to be changed
They are usually mounted on shafts that are 90 degrees
apart, but can be designed to work at other angles as well The teeth on bevel gears can be straight or spiral locomotives, marine applications, automobiles, printing
presses, cooling towers, power plants, steel plants,railway track inspection machines, etc.
3/8/2014 Dr. Nouby M. Ghazaly 17
8/12/2019 Theory of Machines -Lecture1
18/30
Spiral Bevel Gears
Same advantage over bevelgears as helical gears haveover spur gears!!
Teeth at helix angle Very Strong Used in rear end applications
(see differentials)
3/8/2014 Dr. Nouby M. Ghazaly 18
8/12/2019 Theory of Machines -Lecture1
19/30
Differential Gear
The differential gear is used to help cars turn corners. Thedifferential gear (placed midway between the two wheels) allowsthe wheels to turn at different speeds while providing the sametorque to both wheels.
3/8/2014 Dr. Nouby M. Ghazaly 19
8/12/2019 Theory of Machines -Lecture1
20/30
Bevel Gears
Gear axis at 90
, based on rolling cones Advantages
Right angle drives Disadvantages
Get axial loading which complicates bearings andhousings
3/8/2014 Dr. Nouby M. Ghazaly 20
8/12/2019 Theory of Machines -Lecture1
21/30
Worm gears
Worm gear sets consists of a helical gearand a power screw (worm), used totransfer motion between non-parallel andnon-intersecting shafts.
Worm gears are used when large gear reductions areneeded. It is common for worm gears to havereductions of 20:1, and even up to 300:1 or greaterMany worm gears have an interesting property that no
other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm
Worm gears are used widely in material handling andtransportation machinery, machine tools, automobilesetc
Worm and wheel 3/8/2014 Dr. Nouby M. Ghazaly 1. 21
8/12/2019 Theory of Machines -Lecture1
22/30
Worm and Worm gear
3/8/2014 Dr. Nouby M. Ghazaly 22
8/12/2019 Theory of Machines -Lecture1
23/30
Advantages &Disadvantageof Worm Gears
Gears that are 90 to eachother
Advantages
Quiet / smooth drive Can transmit torque at right
angles No back driving Good for positioning systems
Disadvantage Most inefficient due to
excessive friction (sliding) Needs maintenance Slower speed applications
worm
worm gear
3/8/2014 Dr. Nouby M. Ghazaly 23
8/12/2019 Theory of Machines -Lecture1
24/30
Rack and pinion gearRack and Pinion sets a special case ofspur gears with the gear having an infinitelylarge diameter, the teeth are laid flat.
Rack
Pinion
The rack and pinion gear isused to convert between rotaryand linear motion.
3/8/2014 Dr. Nouby M. Ghazaly 1. 24
Radial drilling machine spindle movementwith rack and pinion arrangement
8/12/2019 Theory of Machines -Lecture1
25/30
Rack and pinion
Rack and pinion gears areused to convert rotation(From the pinion) into linear
motion (of the rack) A perfect example of this is
the steering system on manycars
3/8/2014 Dr. Nouby M. Ghazaly 25
8/12/2019 Theory of Machines -Lecture1
26/30
Summary Spur Gears
Simplest of the gears Used to connect parallel
shafts Simple shape Low cost No thrust loads from teeth
engagement
Helical Gears
Smooth operation as itresults in gradual gearengagement
Could connect parallel ornon parallel shafts
Higher thrust loads fromteeth reaction forces
3/8/2014 Dr. Nouby M. Ghazaly 26
8/12/2019 Theory of Machines -Lecture1
27/30
Summary Bevel gear
Could be used to connecttwo shafts that are at anangle
The teeth may be straight orhelical
Two gear have conicalsurfaces
Worm & wheel
Very low transmissionratios
High torque transmission High Friction loses Used in power steering
systems, presses, rolling
mills3/8/2014 Dr. Nouby M. Ghazaly 27
8/12/2019 Theory of Machines -Lecture1
28/30
Summary
Rack & pinion
Converts the rotational
motion into linear motion Could have straight or bevel
teeth Provides less backlash Greater feedback
3/8/2014 Dr. Nouby M. Ghazaly 28
8/12/2019 Theory of Machines -Lecture1
29/30
Report 1
APPLICATIONS OF DIFFERENT
TYPES OF GEARS
3/8/2014 Dr. Nouby M. Ghazaly 29
8/12/2019 Theory of Machines -Lecture1
30/30
Questions?