LN-3
Agricultural Machinery
AG31001
Elements of mechanical rotary
power transmission most
common in agriculture
Mechanical Rotary Power Transmission
Dr. Peeyush Soni
Associate Professor
Department of Agricultural & Food Engineering
Indian Institute of Technology Kharagpur
1.
2.
3.
4.
5.
Bearings and Seals
V-belt drives
Chain and Sprocket drives
Universal joints
Power-Take-Off drives
soni@iitkgp.ac.in
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Mechanical rotary power transmission
Mechanical rotary power transmission
Bearings on agricultural implements…
Required to operated under extremely dusty or dirty conditions
Development of suitable
bearings, seals and lubricants
has been a real challenge
Sealed, factory-lubricated
ball bearings (with no
provision of re-lubrication)
Bearings and Seals
… are extensively used on most harvesting equipment.
High initial cost is justified by reduced R&M cost and
daily servicing time
Provision of re-greasing may have some merit where
excessive heat breaks down the grease; however, there are
issues of:
§ using incorrect grease type,
§ contamination of grease from dirt on the fitting or the gun,
§ collection of dirt/dust around the seal lips
… needed on axles of ground driven rotating
components as well as in power-transmission
systems
Load capacities of Anti-friction Bearing (Ball/Roller/Taper/Needle)
3
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Mechanical rotary power transmission
Self-alignment of bearings on open shafts is an important feature in
agricultural operations
… to compensate for manufacturing tolerances and variable
deflection of supporting members
Self aligning mountings:
Plain cast-iron sleeve body fitted
loosely in a hole in a plate to a sphericalOD ball bearing held in stamped flanges
Turnnion support for bearing housing
Bushing
(Plain Bearing)
Bearings
Anti-friction (Rolling Contact)
Rolling elements placed between the
Consisting of a shaft rotating in a hole, comprising just a
bearing surface and no rolling elements. There are several turning and stationary races prevent
specific styles: bushing, journal bearing, sleeve bearing
sliding friction. Two main types:
solid sleeve Flanged
bushing
bushing
Bronze bushed
journal bearing
Self aligning
support
Not capable of taking thrust
load, unless supported with
circumferential ribs or endflanges
Clenched
(or clinched)
bushing
Ball bearing: designed primarily for radial loading
Roller bearing: High radial load capacity but no
end-thrust. Suitable for low-speed (axle of see d drill).
They’re more sensitive than ball bearings for
misalignment, dirt and grit.
Needle b earing: roller bearing with
more number of small-dia rollers without
a cage or spacer. Exceptionally high
load capacity at low peripheral speeds.
Well suited to applications involving
oscillating motion.
Needle
bearing
Special bearing: a) Disk harrow bearing:
Heavy radial and thrust loads at low speeds,
and operate under dirt. Self-aligning
mounting and effective seals are must.
Bronze, Oil-impregnated metal, Hardened steel, Available with either square or round holes.
b) Tine-bar bearing: on the reel of a sideWhite cast iron, Oil-soaked wood, Plastics
delivery hay rake
Tapered roller
bearing: Takes
both radi al and
thrust loads
depending on
taperness
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Mechanical rotary power transmission
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Single V-belt
Mechanical rotary power transmission
Multiple V-belt
Banded V-belt
These matched sets are used on drives having
high power requirements, and pulsating loads
Matched set of conventional
belts with a thin tie band
connecting their tops.
Tying together…
• minimizes lateral belt whip,
• improves load distribution
among the belts
V-Belt Drives
MercedesBenz Serpentine
Belt Diagram
• Extensively used in agricultural machinery applications where it is
not necessary to maintain exact speed ratios.
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Mechanical rotary power transmission
V-belt transits a given power with less shaft pull than a flat-belt drive,
because V-belt wedges into the sheave grooves
V-belt can be operated with small arcs of contact (as in close-center shaft
arrangements) with large shaft-speed ratios
In agriculture, a single belt often drives several components (Serpentine drive). V-belt
permits considerable latitude in possible orientation and arrangement of shafts
V-belt in Agriculture vs Industry
Prefix H: distinguishes agricultural
V-belts from industrial V-belts.
Agril V-belt loadings can be higher
than their corresponding industrial
application
Cross-sectional sizes of both kinds are the same; but
construction of agri V-belts is stronger and rugged
(to withstand
• excessive shock loads,
• heavy pulsating loads, and
• harsh working conditions)
3 types of V-belts, esp. designed
for agricultural machines
1. Agricultural V-belt
Trapezoidal
section.
Included angle ~
300 - 400
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2. Agricultural double V-belt
3. Adjustable speed
V-belt
Mechanical rotary power transmission
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Adjustable-pitch V-belt sheave has
provision for moving one face axially
w.r.t. the other face, thus changing the
radius at which the belt operates
Mechanical rotary power transmission
Mechanics of V-Belt Drives
Agricultural V-Belt Cross-Sectional Dimensions
V-belt transmits power by virtue of difference in belt tension
between the point at which it enters a sheave and the point at
which it leaves
ΔT is developed through friction between the belt sidewalls and
the sides of sheave groove.
The wedging effect (as the belt is pulled into groove bcoz of belt
tension) greatly increases the potential driving force.
As a belt tends to conform to the sheave curvature, outer section
stretches and inner section is compressed.
Neutral axi s is determined by the position of the load-carrying cords within the belt crosssection. Neutral Axis establishes the pitch-diameter of sheave
Tension difference (ΔT) or Effective Pull,
that is required to transmit the load at each
driven sheave
−
ASAE Standard S211.5
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Mechanical rotary power transmission
= 1000.
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Mechanical rotary power transmission
Tension Ratio (R)
If R is too great, belt slippage will be excessive
For properly designed drive, slippage should not exceed 1 to 2%
If R is too small, unnecessarily high tensions will be
needed for a given effective pull, thereby reducing belt life
The maximum allowable Coefficient k
tension ratio (Ra)
reflecting friction and wedging effect
=
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=
k~0.512
Arc of contact,
rad (=deg x π/180)
• Gears: Constant speed-ratios, Close-center, Intersecting
or crossing shafts, Enclosed for protected lubrication
• Chain drives: Parallel shafts with moderate center
distance, Constant speed-ratios, Usually open for
external oiling
Chain & Sprocket
Drives
For V-belt and V-sheave,
θ=π, most assumed Raπ =5
When arc of contact is less (θ<π), Ra is also
less, thus requiring higher values of tensions
for a given effective pull or power
15
Mechanical rotary power transmission
Advantages of Chain Drives
Chain Nomenclature
• Chain drives, unlike belt drives, do not slip or creep.
• There is no power loss due to slippage; therefore, chain drives are more efficient than belt
drives.
• Chain drives are more compa ct than belt drives. A chain drive, for a given capacity, is narrower
than a belt, and the sprockets are smaller in diameter than the belt sheaves.
• Chain drives are more practical for slow speed drives.
• Chains can operate effectively at high temperatures.
• Chains do not dete riorate due to oil, grease, sunlight, or age.
• Chains withstand chemicals a nd abrasive conditions.
• Chains can operate in wet conditions.
• Chains are effective when several shafts are to be driven from a single sha ft, as positive timing
between the driven shafts is usually re quired.
• Chain drives are simpler and less costly than gear drives.
Limitations of Chain Drives
• Chain drives cannot be used where the drive must slip.
• Chain drives cannot accept much misalignment.
• Chain drives usually require frequent lubrication.
• Chain drives are noisy and can cause v ibration within the machine.
• Chain drives do not have load capacities or service life characteristics equa l to those of gear drives.
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Mechanical rotary power transmission
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Mechanical rotary power transmission
Sprocket
Nomenclature
Types of drive chain common on
farm machines
§
§
§
§
Strands: 2, 3, 4
Standard-pitch roller chain
v = 0.5 to 20 m/s
Well-suited for heavy loads requiring a compact drive
Oil-bath lubrication is needed for high -speed operation
Not suited for Agril machines; several times as expensive as steel detachable chains
Double-pitch roller chain
§
§
Multiple Strands Chain
§
Uses the s ame diameter pins, bushing and rollers, same thickness of link
plates as standard-pitch roller chain, but the side plates have twice the pitch
They have same strength and precision as corresponding standard-pitch
chains, but less mass; Less expens ive than that the s tandard-pitch
Double-pitch d rive chain is used in place of standar d roller chain when
speeds are low, loads are light, and center distances are excessively long
Detachable link chains
§
§
§
§
§
Used both for transmitting power and in conveyors
and elevators
Least expensive type of chain
Well-suited for moderate loads at speed < 2 – 2.5 m/s
They are s.t. more wear than r oller chains due to
loose-fitting, open hooks.
They are not lubricated
Melleable-cast-iron,
detachable link chain
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Mechanical rotary power transmission
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Pressed-steel,
detachable link chain
Mechanical rotary power transmission
Load capacity of chains:
In general, it is based upon the rate of wear rather than the ultimate strength.
As chain wears, the pitch length i ncreases, and the chain rides farther out on the sprocket
teeth
Wear is due to hinge action as chain engages or leaves a sprocket
Rate of wear is directly related to chain speed, and inversely related to chain length
à That’s why speed-ratios should not exceed 10 to 1 (std. pitch roller chain)
6 to 1 (other chains)
Overload Safety
Devices
for rotary drives
Pull required for a given power and speed,
In many types of farm machinery, a single power source drives
various components that have widely differing power requirements,
and subject to varying degrees of possible overload
Required pull, N
−
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= 1000.
Mechanical rotary power transmission
Overload Safety Devices
3 General types of safety devices
commonly used in rotary drives:
A. Shear Devices
A-1: Shear key between shaft and hub
Simple and relatively inexpensive
Sheared element must be replaced after each overload
Not suitable for drives where frequent overload occurs
Shear devices can be designed for almost any desired load rating (selection of
material and size of pin)
§ Removal of the hub from the shaft is necessary to replace shear key
§
§
§
§
Shearing of
replaceable member
Principle of inclined
plane
Usually brass key
with tapered shaft
and bore
Friction
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Mechanical rotary power transmission
A-2: Diametral shear pin through hub and shaft (gives double shear)
Mechanical rotary power transmission
A-3: Flange-mounted shear pin parallel to shaft
T
Shaft,
2r, D
Hub,
2r1, D1
This shear-pin is the most easily
replaced, but the unit is more costly
than a diametral pin
Pin, d
The torque at which a flangemounted shear pin will fail is
The torque at which a diametral shear
pin will fail is
Double shear
=2 (
4
Shaft Torque,
N-m
distance of shear
plane from the
shaft center i.e.
shaft dia
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Mechanical rotary power transmission
Shear-pin dia
=
(
4
Shaft Torque,
N-m
Distance b/w
Shear-pin dia
shaft center and
shear-pin center
)
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Mechanical rotary power transmission
)
Driving
shaft
B. Jump Clutch
Spring loaded
corrugated coupling
C. Friction Devices
Driven
shaft
A properly designed belt drive can serve as a friction safety device!
Although its performance is affected by variations in belt tension and belt slip
It has automatic-resetting feature
It has rounded, mating jaws or corrugations
that are held together by an adjustable spring.
A
B
Spring
adjusment
Single-plate clutches with two friction surfaces
Part A is keyed to driving shaft, and part B
(driven) is free to rotate on the shaft when
overload occurs.
Spring pressure is
adjusted to drive normal
loads, but slip when
overload
When load exceeds the setting of the unit (torque limiter),
operator is warned audibly
Jump clutches are more expensive than shear devices, and
not suited to large loads (due to excessive physical size
required)
Spiral jaw clutch
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Friction clutches are very
effective in protecting a
drive from high-frequency
peak torques
Principle of friction clutch
But excessive slipping
overheats the friction plates
When jumping, they impose high shock loads upon the
drive system
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Mechanical rotary power transmission
A universal joint (or Cardan) is a joint or coupling in a
rigid shaft that allows the shaft to "bend" in any direction
Mechanical rotary power transmission
Some Terminology
α Joint angle
ω1 Input (driving) angular velocity (rad/s)
ω2 Output (driven) angular velocity (rad/s)
β1 Angle of rotation (momentary) of Input shaft
from initial posi tion (rad)
β2 Angle of rotation (momentary) of Output
shaft from initial positi on (rad)
Universal Joints
spider
1. Single joint
2. Multiple joint combinations
28
Source: https://www.crawlpedia.com/u_joints .htm
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Mechanical rotary power transmission
Single joints
The basic parts of universal joint
Angles of rotation of the two shafts
( 1, 2) are related to the joint angle (α)
tan
=
tan
cos
α
k
tan
= tan (
cos
Universal joint under a straight mo tion
Peak lag occurs when the input
shaft is past 450 plus by an
amount equal to half the peak
lag (indicated by broken line in lower half)
The spin of the cross makes a huge difference in the
speed of the output shaft. The cross has 2 kinds of
motion: rotation and spin. When the cross is spinning as
well as rotating, the velocity of the output shaft will have
an added effect. For the first 900 of the input shaft
rotation, the green axis spins to its maximum angle. The
forward s pin aids and changes the o utput shaft rotation
−
1)
Source: www.learnengineering.org
2
Forward spin of the shaft
during the first 90 0
1
But for the next 90 degrees, it shoul d spin back to the
initial zero position. The reverse spin will have an
opposite effect on the output shaft rotation.
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Peak lead occurs when the input
shaft is at 1350 minus by an
amount equal to half the peak
lag (indicated by broken line in upper half)
(
The ends of universal joint turn in
different planes. The shaft connecting
the green ends should spin to
accomplish this movement
Angular displacement of the output
shaft during 180 degrees turn
Mechanical rotary power transmission
A single joint operating at an angle, does NOT
deliver uniform angular output velocity ω2
The output shaft has a fluctuating speed.
More the angle between the shafts more will
be the speed fluctuation.
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Motion and Torque
characteristics of a single joint
Mechanical rotary power transmission
If a single joint is deflected by angle α (joint angle) and
rotated by ß1 then the output shaft differs from rotation
angle of the input shaft.
Wh en there is a joint angle, motion of
the output yoke doesn’t follow the
motion of the i nput yoke in terms of
ang ular displacement, velocity, and
acc eleration.
The amount of variation b/w the input
and output motions depends on the
operating angle (joint angle).
The angular displacement of the output
yoke ( 2) during one revolution lags and
leads the input yoke twice.
The maximum angular acceleration/
deceleration coincides with the
maximum lag and lead angles,
respectively
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Mechanical rotary power transmission
)
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Mechanical rotary power transmission
ω2
cos
=
ω1 1 − sin 2 . cos 2
Angular
velocities
ratio
The max speed of driven (output) shaft
=
2
1
=
1 − sin2
=
1
The min speed of driven (output) shaft
Condition for equal
speeds of the shafts
tan
The max fluctuation of output
speed max(ω 2) - m (ω2 )
Angular Acceleration of
the output Shaft
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Mechanical rotary power transmission
Exercise:
Two shafts are connected by a universal joint. The driving shaft rotates at a
uniform speed of 1200 rpm. Determine the greatest permissible angle between the shaft
axes so that the total fluctuation of speed does not exceed 100 rpm. Also calculate the
maximum and minimum speeds of the driven shaft.
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Mechanical rotary power transmission
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ω2
= ± cos
max(ω2) -
ω2 = ω1α 2
ω2 cos . sin 2 . sin
= 1.
(1 − sin 2 . cos 2 )2
Max angular Acceleration of the
output Shaft, at corresponding
2 sin 2
Mechanical rotary power transmission
Exercise:
cos
1
=
(2 − sin 2
Two shafts with an included angle of 160° are connected by a Hooke’s joint.
The driving shaft runs at a uniform speed of 1500 rpm The driven shaft carries a flywheel of
mass 12 kg and 100 mm radius of gyration. Find the maximum angular acceleration of the
driven shaft and the maximum torque required.
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Mechanical rotary power transmission
1
)
Multijoint Combinations
Bearing loads on input and output
shafts with Z-Arrangement
When 2 univers al joints are connec ted in series, the angular displacement and velocity fluctuations
will cancel (condition of equal speeds) IF (a) the joint angles are equal (output and input shafts
make equal angles with the intermediate shaft), and (b) the axes of the output and input
shafts are coplanar
Driveline-center part stressed in bending
Double Universal Joint
Constant velocity ratio: Double Hooke’s Joint
If a constant velocity input gives fluctuating output, a
fluctuating input will gi ve a constant velocity output. Thus,
the double universal joint acts as a constant velocity joint.
Use of double uni versity joint in eliminating jerky motion
Source: www.lear nengineering.com
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Mechanical rotary power transmission
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Mechanical rotary power transmission
Bearing loads on input and output
shafts with W-Arrangement
In W-arrangement, an additional force, “S“ is introduced, caused
by the additional moments TZII acting in the same direction.
Input and output shaft stressed in bending
Power-Take-Off Drives
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Mechanical rotary power transmission
Lift
Arms
PTO Adapters & Extenders
Lift Rods
Lower
Lift Links
Sway
Chain
PTO Adapter, Clamp Type,
1-3/4" 20 Spline Female,
1-3/8" 21 Spline Male
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Mechanical rotary power transmission
power take-off
PTO
external shaft on the rear of the tractor to provide rotational power to implements
(ISO:500 definition)
Swinging
drawbar
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Mechanical rotary power transmission
Standardization of PTO Drives
Why standardization?
Easy attachment and interchangeable
use of PTO-driven implements with
various makes and models of tractors
ASAE and ISO Standards
ISO 500: rear-mounted PTOs
on agricultural tractors with a track width
of more than 1 150 mm
Independently controlled PTO (introduced in 1940 ) greatly increased its versatility
in comparison with the Transmission-driven PTO
PTO used extensively on:
ü
ü
ü
ü
ü
ü
Harvesting equipment (trailed / mounted)
Sprayers
Rotary or vibratory tillage implements
Pull-type field forage choppers
Corn pickers
Stalk cutters and shredders
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Mechanical rotary power transmission
The tractor rear PTO is classified into four types
PTO type
Nominal
diameter,
mm
Number and
type of
splines
Nominal PTO
rated rotational
speed, rpm
Recommended
power at rated
engine speed , kW
1
35 [1⅜]
6 straight
540
<65
2
35 [1⅜]
21 involute
1000
<130
3
45 [1¾]
20 involute
1000
<300
4
57.5
22 involute
1000
<450
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Mechanical rotary power transmission
ASAE Standard S203.8
540 rpm
Type-1
1000 rpm
Type-2
1000 rpm
Type-3
Shaft dia, mm
35 [1⅜]
35 [1⅜]
45 [1¾]
A, mm
356
406
508
C, mm
330 - 432
330 - 432
432 - 533
D, mm
152 - 305
152 - 305
203 - 254
B, mm
-25 to +127
-25 to +127
-25 to +127
5: P TO
6: master shield
7: Drawb ar
External, straight-sided spline
dimensions — Type 1 (source: ISO:500-3)
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External, involute spline
dimen sions — Type 2 (source: ISO:500-3)
Mechanical rotary power transmission
Telescoping PTO shaft with integral safety shield
Standardized locations for the PTO shaft and drawbar hitch point on agricultural tractors.
Hitch point is directly beneath the extended center line of the PTO shaft
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Mechanical rotary power transmission
PTO Drives with TWO & THREE Universal Joints
Fixed-length shaft b/w front 2 joints;
Telescopic shaft b/w 2 re ar joints
e.g. ASAE Standard
dimension 356 (14”)
shaft is used with 540
rpm PTO having 356
mm from h-point to the
end of PTO shaft
◙
◙
A
Angle
between
implement
and tractor
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Mechanical rotary power transmission
The dim A is greater for
Type-2, 3 PTOs (1000 rpm);
so the problem of unequal
angles is minimized or
eliminated for the higher
PTO speed systems
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Angles in u-joints,
Two u-joint drive
Angles in front u-joints,
Three u-joint drive
Front joint
Second joint
Front joint
00
0
0
0
0
300
16
14
12
18
500
27
23
21
29
700
38
32
33
37
900
50
40
54
39
Mechanical rotary power transmission
Second joint
PTO Drive with Offset
If the driven shaft of implement is offset from the centerline of PTO shaft so that the normal joint angle of
one or both the intermediate shafts is > 15 – 20 0 from the PTO shaft, serious fluctuations may occur
during sharp turns
Two possible arrangements for
obtaining the offset:
1. Joints phased
2. Joints not phased
Telescopic shaft
Both theoretically provides uni form velocity
of driven shaft when the implement and
tractor are in line.
Fixed shaft
1. Joints phased
2. Joints not phased
Provides much less fluctuations
on sharp turns – due to having
smaller maximum joint angles
Plan views of two arrangements of a 3 u-joint offset PTO drive
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Mechanical rotary power transmission