Power transmission elements and units

1. GAZIANTEP UNIVERSITY
NATURAL AND APPLIED SCIENCE INSTITUTE
MECHANICAL ENGINEERING
CONSTRUCTION AND MANUFACTURING DIVISION
PROJECT OF GEAR AND PLANETARY DRIVES
REVIEWED BY PROF.DR.NİHAT YILDIRIM
SUBMITTED BY: BAHADIR KARBA

2. Contents
• Description Of The Gear and Planetary Drives
• Types of Gear and Planetary Drives
• Areas and Examples Of Use in different industries of Gear and Planetary Drives
• Basic functioning of Gear and Planetary Drives
• Component of Gear and Planetary Drives
• Design principles of Gear and Planetary Drives
• Numerical Design Examples Of Gear and Planetary Drives
• Design principle of components of Gear and Planetary Drives
• Numerical design examples of component of Gear and Planetary Drives
• Discussion

3. GEAR DRIVESDescription:
All drive systems require a drive gear.
The drive gear is the main transfer from the power source to the driven gear.
A belt from the drive gear to the driven gear is a "belt driven" system.
Another option is the "chain driven" system. The "chain driven" system uses a chain from the drive
gear to the driven gear.
The "gear drive" system is direct gear-drive. The drive gear is directly meshed with the driven gear.
The most reliable means for changing shaft speed remains a mechanical variable-speed transmission.
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 that transmits rotational force to another.These
drives are used to provide a variable output speed from a constant-speed power source or to provide
torque increase for a variable-speed power source.
Gear drives are used in transmissions, rear ends and transfer cases; at times the drive gear will be
smaller than the driven gear. Different gear ratios enable the transmission to shift to lower or higher
rpm speeds.

4. What Are Gears Used For?
Gears can serve as an efficient means to reverse the direction of motion, change rotational speed, or
to change which axis the rotary motion is occurring on. The sizes of the gears usually depend on the
desired gear ratio and the shaft upon which the gears will be mated.
How Do Gears Work?
1. Reversing Direction of Motion: Any two gears that come into contact with one another will
naturally produce an equal and opposite force in the other gear. For example, as the smaller gear
pictured below moves clockwise, the larger gear will naturally move counter-clockwise.
Any shaft attached to the respective gear will rotate in the direction of the gear it is attached to.
2. Changing Rotational Speed: Rotational speed is adjusted through the use of a "gear ratio."
The gear ratio is the ratio of the radius of the drive or "input" gear (the one that is powering the
interaction between the two gears) to the radius of the "output" gear. It can also commonly defined as
the number of teeth on the input gear to the number of teeth on the output gear.
The gear being turned by the motor is referred to as the “driver” gear while the last gear, often the
output gear, in the system is referred to as the “driven” gear. Any additional gears in the drive train
are “idler” gears.
3. Changing The Axis of Rotation: Perhaps the most common gear for changing rotational axis is the
bevel gear (seen below). The bevel gear is commonly used in vehicle differentials to rotate the
motion provided by the engine 90 degrees in order to drive the wheels along their proper axis.

5. Types Of Gear Drives
Classification of Gears: Classification of
gears can be done according to the relative
position of the axes of revolution into
three types.
I. Gears for Parallel shafts: Spur
Gears, Helical Gears, Herringbone
Gears, Rack and Pinion
Efficiency (%) 98.0 – 99.5
I. Gears for Intersecting Shafts:
Straight Bevel Gears, Spiral Bevel
Gears,Screw Gear,Zerol Bevel Gear
Efficiency (%) 98.0 – 99.0
II. Gears for Skew Shafts (Nonparallel
And Nonintersecting):
HypoidGears,WormGears
Screw gear (Efficiency 70.0 – 95.0 %)
Worm gear (Efficiency 30.0 – 90.0 %)

6. Advantages of gear drives
• Positive drives.
• High transmission efficiency.
• High velocity possible, even up to 60:1.
• Velocity ratio will remain constant throughout.
• Used for low, medium and high power transmission.
Disadvantages of gear drives
• Require lubrication.
• At very high speeds, produce noise and
vibrations.
• Manufacturing of gears is costly.
• The large number of gear wheels in gear trains
increased the weight of machine.
• Not suitable for shafts having large centre
distance.
• So as usual,designers has to be logical and
optimal during selection of drive.

8. Spur Gears:
• Straight Spur gears are the simplest form of
gears having teeth parallel to the gear axis.
The contact of two teeth takes place over the
entire width along a line parallel to the axes
of rotation. As gear rotate , the line of
contact goes on shifting parallel to the shaft.

9. Helical Gears:
• In helical gear teeth are part of helix
instead of straight across the gear
parallel to the axis. The mating gears
will have same helix angle but in
opposite direction for proper mating.
As the gear rotates, the contact shifts
along the line of contact in in volute
helicoid across the teeth.

10. Herringbone Gears:
Herringbone gears are also known as Double
Helical Gears. Herringbone gears are made
of two helical gears with opposite helix
angles, which can be up to 45 degrees.

11. Rack and Pinion:
• In these gears the spur rack can be
considered to be spur gear of infinite
pitch radius with its axis of rotation
placed at infinity parallel to that of
pinion. The pinion rotates while the
rack translates.

12. Straight Bevel Gears:
• Straight bevel gears are provided with
straight teeth, radial to the point of
intersection of the shaft axes and vary in
cross section through the length inside
generator of the cone. Straight Bevel
Gears can be seen as modified version of
straight spur gears in which teeth are made
in conical direction instead of parallel to
axis.

13. Spiral Bevel Gears:
• Bevel gears are made with
their teeth are inclined at an
angle to face of the bevel.
Spiral gears are also known as
helical bevels.

14. Zerol Bevel Gears:
• The teeth of "Zerol" bevel gears are curved
but lie in the same direction as the teeth of
straight bevel gears. "Zerol" bevel gears are
similar to spiral bevel gears except the
"Zerol" gears have zero spiral angle and are
manufactured on the same machines as
spiral bevel gears.
• As in straight bevel gearing, "Zerol" bevel
gears have no inward axial thrust. Their zero
degree spiral angle produces no thrust load.
These two types of bevel gearing are
interchangeable in equipment; thus, no
changes are required for thrust bearings.

15. Hypoid Gears:
• The Hypoid Gears are made of the frusta of
hyperboloids of revolution. Two matching
hypoid gears are made by revolving the
same line of contact, these gears are not
interchangeable.

16. Worm Gears:
• The Worm Gears are used to connect
skewed shafts, but not necessarily at
right angles. Teeth on worm gear are
cut continuously like the threads on a
screw. The gear meshing with the
worm gear is known as worm wheel
and combination is known as worm
and worm wheel.

17. Gear drives are
commonly classified
according to end use:
• Automotive transmissions: Used as
main transmissions in cars, trucks,
farm machinery, and earth-moving
equipment. Usually provide from four
to 10 speeds.

18. Auxiliary
transmissions:
• Usually installed behind the main
transmission to increase available ratios.

19. Transfer cases:
• Provide additional power outlets (as in a
four-wheel-drive vehicle) or provide
offset from normal drivelines.

20. Power takeoffs:
• Usually mounted beside main
transmission and driven by an
additional gear in that transmission.
Similar to a transfer case.

21. Marine gears:
• Transmissions carrying power to the
propeller on a marine drive. Differ
from other transmissions in that
they generally provide single
forward and reverse speeds and use
friction-type shifting clutches.

22. Hydraulic drives:
• Gearboxes connecting power source
and hydraulic pumps in hydrostatic
drives.

23. Industrial
transmissions:
• A broad category applying to any
transmission powering machinery
other than that described above.
Many have integral power
packages, such as electric or
hydraulic motors, or they may be an
integral part of driven components.

24. • The first consists of one input and two outputs. The automobile
differential is the best example here. The important factor in this type of
application is the two outputs are connected mechanically. In
automobiles, the connection is the road. The differential automatically
balances speeds and torques between the two wheels because only the
sum of the wheel speeds is defined by the input speed. That means each
wheel will rotate at the speed required to maintain the predetermined
torque relationship of 1:1 between them.
• The second application type has two inputs and one output. Less well
known than the first, this technique solves industrial problems when the
superimposition of one motion relative to another is required, such as
timing of cutoff, registration control on printing presses, tension control,
and phase shifting on textile industry equipment.
• Differential efficiency is a function of the relative speed of the three
elements. As relative speeds increase, the inherent losses due to basic
gear efficiency, seals, and bearings also increase; thus, efficiency
decreases.
Differentials: A set of gears with three independent, rotating members with a
speed and torque relationship to each other. This definition creates two application types.

25. Components Of Gear Drives
• Bearings
• Shaft: A shaft is a rotating member, usually
of circular cross section, used to transmit
power or motion. It provides the axis of
rotation, or oscillation, of elements such as
gears,pulleys, flywheels, cranks, sprockets
• Axle:An axle is a nonrotating member that
carries no torque and is used to support
rotating wheels, pulleys, and the like.
• Oil-Seal
• O-Ring
• Screws
• Bolts
• Motors
• Coupling
• Gears

26. • Gear Design
• The key step in gear design is the
determination of the allowable tooth bending
stress. For any given material, the allowable
stress is dependent on a number of factors,
including:
• – Total lifetime cycle.
• – Intermittent or continuous duty.
• – Environment – temperature, humidity,
solvents,
• chemicals, etc. Change in diameter and
centre to centre distance with temperature
and humidity.
• – Pitch line velocity.Diametral pitch (size of
teeth) and tooth form.
• – Accuracy of tooth form, helix angle, pitch
diameter,etc.
• – Mating gear material including surface
finish and hardness.
• – Type of lubrication (frictional heat).

28. Example
• A set of Spur gears (Pinion cut from hot rolled BS 08040M steel with HB
180 and gear cut from BS 220 cast-iron) is to be designed to transmit 1.25
kW at a pinion speed of 400 rpm and a speed reduction of 1.5:1
• Use a safety factor of 4 and determine suitable values for:
Modüle:
Pitch diameter:
Tooth numbers:
Face width of the pinion & gear
• Use 20 degrees full-depth teeth with b=1.25m & make necessary
assumptions if required.
Numerical Example Of Spur Gear Mesh Design

29. Steps For Solution:
Two criteria
1)Bending stress fatigue(for pinion&gear)
2)Contact strees fatigue(for pinion&gear)
Bending stress condition:
ng=Se/σ Sut pinion=550 Mpa Sut gear=220Mpa
Gear with Sut=220 Mpa (<Sutpinion) is more critical than the pinion.Thus base bending fatigue design on gear.
Contact Stress:
ng=Wtp/Wt or 1/ng= σH/SH= / CL*CH*Sc
C T*CR

30. Nomenculature Of Design Parameters Conditions&Tables
• Sc=(2.76HB-70) Mpa Surface Fatige strength for Steels
• Cp :Elastic coeffiecent
• CL: Life modification factor
• F: Facewidth 3pc<F<5pc design criteria
• d: Is the pitch circle diameter of the gear in meter
• σ= Wt/(F*m*Y) in lewis equation is used
only for static design and is not accurate
enough for dynamic conditions
• Y :Is the modified from factor
• N: Number of teeth
To prevent requirement requirement
of larger diameter gears
To prevent mal-distribution of tooth
load over face width
• Wt : Is the tangential load
• J: Geometry factor
• Kv: Is the speed factor
• n: Is the rotational speed of the same gear in rpm
• Pressure angle : Nmin= 2/(Sin^2(pressure angle))
• CH: Hardness-ratio factor ;use 1.0 for spur gears
• CT: Temperature factor ;use 1.0 for temp <120°C
• CR: Reliability factor
• SH: Corrected fatiguee strength or Hertzian factor
• I: Is the called the geometry factor
• Ko: Overload correction factor
• Km:Load distribution factor

33. • HBpin=180,HBgear=196 Since HBpin is less tan HBgear the contact
stress design has to be based on pinion.Also
Pinion rotates more.
Bending Stress fatigue design of gear
T<=Se/ng & 3pc<F<5pc T=Wt/(Kv*F*J*m) Wt=Power/linear velocity=1250 watt/(𝜋 ∗ 𝑑𝑝 ∗ 𝑛𝑝/60)
Dp=m*Tp speed reduction is 1.5:1 hence,Tgear=1.5*Tpinion , npinion=400rpm,ngear=400/1.5
Let Tmin=18 is equal to Tpinion=18,Tgear will be =27 Wt=3.3157 Nt (m in meters)

42. m=6,Tpinion=18,Tgear=27,Facewidth=83mm

43. Planetary Gears
• Note that the sun gear, planet pinions, and ring
gear are constantly in mesh. Planetary gearing
or epicyclic gearing provides an efficient
means of obtaining a compact design of power
transmission with driving and driven shafts
parallel to each other. Planetary gear units can
use spur or helical gear tooth forms.
• Planetary gears are suitable for installations
requiring a/an:
• Increase or decrease in speed of the driven
component
• Change in direction of rotation of the output
• Torque increase or decrease
• As shown in Figure 36, planetary gears are
similar to the solar system. The planet pinion
gears or carriers each turn on their own axis
while rotating around the centrally positioned
sun gear. The planet pinion or carrier gears
mesh with the inside gear teeth of the ring gear.
Figure 36: Planetary Gears

44. • The planet pinions are mounted on shafts in the carrier assembly
and can rotate on their axis to walk around the sun gear or the ring
gear.
• When power is applied to drive the sun gear, on either the planet
pinion carrier or the ring gear, the entire planetary system will
rotate as a unit.
• A restraining force (reactionary device) applied to one of the other
two planetary members will hold the system stationary. With no
reactionary device in place, a neutral situation results in the drive
unit.
• When power is applied to one member of the planetary system
and a brake mechanism is applied to restrain a second member
from rotating, the remaining part will become a power output
source as illustrated by the following examples.
• When the sun gear is driven, as shown in Figure 37, and a brake is
applied to the ring gear, the planet pinions walk around the ring
gear, forcing the planet pinion carrier to rotate in the same
direction as the sun gear, but at a slower speed.
Figure 37: Planetary Gear Movement

45. • When the planet pinion carrier is driven,
as shown in Figure 38, and a brake is
applied to the ring gear, the planet
pinions revolve around the ring gear,
forcing the sun gear to rotate in the same
direction at a higher speed.
Figure 38: Planetary Gear Movement

47. Advantages Of Planetary(Epicyclic) Drive
• Compared to conventional gearboxes has
smaller dimensions
• Easier to sort through the constant rounds
of shot
• Greater durability than conventional bikes
in gear
• Easy to achieve high transmission ratio due
to the size
• They have higher gear ratios
Disadvantages Of Planetary drive
• More expensive than conventional production
of gearboxes
• More complex than conventional transmission

48. Do’s & Don’ts
-Calculate planet locations
– Define assembly match marks on drawing.
– Use relative speeds
– Divide torques correctly
– Analyze planets as idlers in simple epicyclic sets
– Check planets for O.D. interference
– Use free-body diagrams
– Rigidly fix all members unless application requires it
– Assume power splits
– Use coupled sets that have internal power
recirculation
– Forget centrifugal loads on planet bearings

50. Planetary Geartrain Analysis
J. Borders
03.11.2009

70. Discussion Gear & Planetary Drive Systems
• As you can see, gear drive systems are widely used in everyday life. because the gearing systems provide high
efficiency power transmission and high power dissipation ratios.
• Even if the production, installation, repair and maintenance of gear drive systems are expensive, the plus points
indicate that this system will protect its future position.
• How do I choose the first question gear box? There are several types of gearboxes manufactured world-wide. One
of the major differences between individual gearboxes is their performance characteristics. Selecting from the
various gearbox types, depends on your application. Gearboxes are available in many ratios, sizes, efficiency, and
backlash characteristics. These design factors will affect the performance and cost of your gearbox. There are many
types of gearboxes including: Bevel, Helical, Spur, Worm, and Planetary.
• these two power transmission system types are used in many industrial applications, as in the past, as well as
creating ideas for new industrial designs.

71. References:
•
http://www.designworldonline.com/energy-efficient-and-sustainable-conveying/
• http://www.dynamarinegroup.com/product_marine-gearbox-supplier-ship-propulsion-system-output-gear-
box_12291.html
• http://www.off-road.com/diesel/tech/offroad-tech-transfer-cases-explained-54200.html?printable
• http://www.free-ed.net/sweethaven/MechTech/Automotive01/AutomotiveSystems.asp?iNum=97
• http://6066gmcguy.com/spicer-5831-b.html
• https://dbsantasalo.com/industries/mining-minerals/bulk-materials-handling/cx-conveyor-drives/
• http://www.mrclutchnw.com/services/differential-rebuilding/
• https://www.myodesie.com/wiki/index/returnEntry/id/3000#Planetary Gears
• https://me-mechanicalengineering.com/classification-of-gears/
• www.geartechnology.com