Power Transmission system

1. Power Transmission Units in Agricultural
Tractors and their Design Concepts
1
Course Instructor: Presented by:
Dr. T. K. Bhattacharya Chelpuri Ramulu
Professor & Head Id.No.-51183
Ph.D. (FMPE)
Department of Farm Machinery & Power Engineering
GBPUA&T, Pantnagar

2. Power Train of Agricultural Tractors

3. Basic Functions of Power Transmission
System
1. To transmit power from the engine to the
rear wheels of the tractor.
2. To make reduced speed available, to rear
wheels of the tractor.
 Operating speed of agricultural tractor is 3-6kmph
3. To alter the ratio of wheel speed and
engine speed in order to suit be field
conditions.

4. Obtain desire speed and torque05101520
1 2 3 4
Gears
Torque,“x1000”Nm
Speed,kmph
5101520
Gear-torque-speed relationship
Low gear – High torque, Less speed
High gear – Less torque, high speed

5. Type Of Gears
Gears are made up of medium carbon or alloy steel
Average transmission efficiency of external gears are 98.5 % and 99% for internal gears.

6. Gear ratio
Gear ratio When two shafts are connected by
gears ,the ratio between the speed of those shafts will
be always constant and this constant ratio is called
GEAR RATIO.
Speed of Driver(N1) No. of teeth in Driven (T2)
------------------------- = --------------------------- = constant.
Speed of Driven(N2) No. of teeth in Driver (T1)

7. Gear Design Consideration
Pitch Diameter of spur gear is determined by following
Equation

8. Helical gears
 Tangential force ( Pitch diameter)
 Thrust force (Helix angle)
 Separating force (Pressure angle)

9. The general range of tooth module for various
gears in drive train
 Transmission gears - 4 to 5
 Power shift planetary gears - 2.5 to 3.5
 Spiral bevel gears - 8 to 12
 Final drive gears - 5 to 7

10. GEAR BOX
Sliding mesh SynchromeshConstant mesh

11. Sliding Mesh Gear Box

13. Constant Mesh Gear Box

17. Synchromesh Gear Box

21. Gear Box Merits Demerits
Sliding Mesh Gear
Box
Highly efficient
Economical
Simple design
Difficult shifting of gear
Need to slow down the
speed while changing gear
Noise in operation
Require highly skilled
driver to change the gear
Constant Mesh
Gear Box
Less noise in operation
Less shifting effort
Less efficient than sliding
mesh gear box
Double declutching is
required for changing of
gears which cause fatigue
of the driver
Synchromesh
Gear Box
Noiseless gear changing
Smooth gear changing
Less vibration
Initial cost is high
More space is required
Precise operation is
required

22. Transmission efficiency

23. Speed reduction in John Deere 5055E

24. Transmission System In Different Tractors
Tractor model
and
manufacturer
Transmis
sion
system
Rated
engine
speed
(rpm)
Number of
speeds
Forward
speed
(kmph)
Reverse
speed
(kmph)
Mahindra 585
DI
Bhoomiputra
Partial
Constant
Mesh
2100 8F+2R 2.9 to 30.9
4.05 to
11.9
John Deere
5050D
Collarshif
t Gearbox
2100 8F+4R
2.97 to
32.44
3.89 to
14.10
Sonalika DI
745 III
Constant
mesh
2100 8F+2R
2.40 to
33.26
Messy
Ferguson
Sliding
mesh
gear
1790 8F+2R 34.2 15.6
FarmtracEPI
50 shakti
Constant
mesh
2000 8F+2R 2.5 to 30.1 3.1 to 12.1

25. Final drive ratio of different tractors
New Holland 3510(Rated Engine rpm-2000) -6.545:1
New Holland 3037(Rated Engine rpm-2000) -5.385:1
New Holland 4010(Rated Engine rpm-2000) -6.545:1
New Holland 4710(Rated Engine rpm-2250) -6.545:1
(Planetary Type Reduction)

26. Gear reduction ration in tractors from engine drive
to final drive
(Engine RPM is 2400 Rear tires size 13.6-28)
Gear Speed (Kmph) Wheel RPM
Gear Reduction
Ratio
A1 1.8 13.65 1:175
A2 2.6 19.71 1:121
A3 4.0 30.33 1:79
B1 5.1 38.67 1:62
B2 7.4 56.11 1:42
B3 11.1 84.16 1:28
C1 11.9 90.23 1:26
C2 17.1 129.65 1:18
C3 25.8 195.62 1:12
AR 3.1 23.50 1:102
BR 8.6 65.21 1:36
CR 20 151.64 1:15

27. Design Consideration of Gearbox
of a Tractor
1. To reduce the size of gearbox, the intermediate shaft should have as
high speed as possible.
2. At any point of time only one set of gears should be in mesh. In other
words, one set of gears must be completely disengaged before the
other starts to engage.
3. The transmission ratio (TR) of a pair of gears in a gearbox should
satisfy following condition. TR ≤ 2:1 and ≥ 1:4 or in other words
0.25 ≤ TR ≥ 2
4. The speed range ratio (Maximum shaft speed divided by minimum
shaft speed) should not be more than 8.

28. 5. In case of sliding gearbox, the centre distance between two
shafts should remain constant or in other words the sum of
number of teeth of meshing gears must be constant.
T1+T2=T3+T4 = Constant
6. In a gearbox same module (m) of the gear set must be used.
7. The minimum difference between the numbers of teeth of
adjacent gears must be 4.
8. The minimum numbers of teeth (in a set for spindle drives)
should be greater than 17 to avoid interference of tooth.

29. Torque Converter
Torque converter is a hydraulic transmission which
increases the torque of the vehicle reducing its speed. It
provides a continuous variation of speed ratio from low
to high.
The key characteristic of a torque converter is its ability
to multiply torque when there is a substantial difference
between input and output rotational speed, thus
providing the equivalent of a reduction gear.

32. Hydrostatic transmission
 Quite costly
 Very inefficient
 A hydrostatic transmission involves conversion of power
between mechanical energy and hydraulic pressure
 Often noisy
Popular in which variable speed control is very important
(Combines)

33. Working Principle

34. Continuously Variable Transmission
Mostly in machine tools and some low power drives

35. FINAL REDUCTION
Bull gear- pinion Planetary gear Big crown wheel
Final reduction
1. Causes further reduction in speed
2. Increase the torque
Final reduction

36. Bull-gear pinion reduction
• Reduction in differential housing
• Mahindra, Swaraj,Sonalika,
• Reduction at rear wheel
• HMT,Escorts
Load comes at one point on drive parts
Noisy operation
Requires more space

37. Big Crown Wheel
Bigger crown wheel
- More effort is required for braking
Found in Ford, TAFE
tractors
Bigger crown
wheel

38. Planetary reduction
1. Equal distribution of load on each gear and axle
2. longer life of gear and axle
3. Compact
4. Quieter operation
5. Latest design being used world over

40. Planetary Gear Working

41. Planetary Ratio
ns=the rpm of the sun gear
nc=the rpm of the carrier
nr=the rpm of the Ring gear
Nr=the number of the teeth in ring gear
Ns=the number of the teeth in sun gear
 If the ring gear is fixed then nr =0 (Sun gear is the input and Ring
gear is output)
 If the sun gear is fixed then ns =0 ( Ring gear is the input and
Planetary gear is output)
 If the planetary gear is fixed then nc =0 (Sun gear is the input and
Ring gear is output)
ns=nc-(nr-nc)Nr/Ns

42. Conclusion
 Incase of manual transmission, the synchromesh
gear box is better than the others
 The common types of gears used in transmission of
agricultural tractors are helical, spur and bevel gears
 The most better final drive is planetary gear system
 The approximate gear reduction in tractors from
engine drive to final drive are 1:175 (at lower gear)
to 1:12 ( at higher gear)

43. References
http://ecoursesonline.iasri.res.in/mod/page/view.p
hp?id=2284
http://smallengineinformation.com/?page_id=323
• Continuously variable tractor transmissions Karl Th.
Renius and Rainer Resch
• www.youtube.com (Learn engineering, JAID, how
machine works.com and www.mekanizmalar.com)

44. Thank You !

45. Questions Hour
1. What is pressure angle
Ans. Pressure angle in relation to gear teeth, also known as
the angle of obliquity, In involute teeth, it is defined as
the angle formed by the radial line and the line tangent to
the profile at the pitch point.
The most common pressure angle is 200 . Formerly, a
pressure angle of 14.50 was also used
2. Why spur gear used sliding mesh gear box
Ans. The main principle of working of this gear box is
that Sliding so the spur gear is used because they
having straight tooth cut.

46. 3. What is addendum and dedendum
Ans. The addendum is the radial distance between
the top land and the pitch circle .
The dedendum is the radial distance from the
bottom land to the pitch circle.
4. Whether the differential system is reduction unit
or not
Ans. Yes. It is also a gear reduction unit. The
approximate gear reduction at differential is about
25:1.
5. How to indicate the size of the gear
Ans. The size of a gear is indicated by tooth module
(Pitch circle diameter/No.of teeth on a gear)