EFFECTS OF SURFACE CONDITION ON THE TRACTIVE
PERFORMANCE OF SMALL AGRICULTURAL TRACTOR ON
BANGKOK CLAY SOIL
by
Jannatul Ferdous
A thesis submitted in partial fulfillment of the requirements for the
degree of Master of Engineering in
Agricultural Systems and Engineering
Examination Committee:
Nationality:
Previous Degrees:
Dr. Peeyush Soni (Chairperson)
Prof. Athapol Noomhorm
Dr. Wattanaporn Meskuntavon
Dr. Alex Keen (External Expert)
Bangladeshi
Master of Science in Irrigation and Water Management
Bangladesh Agricultural University
Mymensingh, Bangladesh
Bachelor of Science in Agricultural Engineering
Bangladesh Agricultural University
Mymensingh, Bangladesh
Scholarship Donor:
Government of Norway
Asian Institute of Technology
School of Environment, Resources and Development
Thailand
May 2011
ABSTRACT
The aim of this research is to investigate the effects of moisture and surface condition of
soil of a small agricultural tractor in 2WD and 4WD on Bangkok clay soil. Four torque
transducers was developed, manufactured and assembled to the four wheel of tractor to
measure the wheel force which occurred during testing. One sting port was developed and
assembled to a shear box and tractor for determining the soil deformation for both
laboratory and field test. Furthermore four pulse sensors were connected to four wheel of
tractor to measure wheel speed. To measure wheel slip one dynamo was connected to the
front wheel of loaded tractor. Tractor drawbar pull was measured by using load cell
connected to the drawbar of test tractor. Test was done on the agricultural field and
laboratory of the Agricultural and Systems Engineering department. From the experiment
highest rolling resistance was found 2.803 kN for soft plastic soil on a bare surface for the
tractor in 2WD and lowest was 1.325 kN for 4WD on the grass surface for hard top soil
with soft subsoil. Wheel thrust was found highest (10.58 kN) for hard soil grass surface for
the tractor in 4WD and lowest (5.295 kN) for soft plastic soil bare surface in 2WD. The
range of deformation modulus was 0.0013 to 0.0052 m in shear box test. The range of
deformation modulus from all tests for both front and rear wheels was 0.020 to 0.066 m in
field test. For bare surface deformation modulus for rear wheel was 0.057 m and 0.051 m
for front wheels. Similarly, 0.038 m and 0.03 was the deformation modulus for the grass
surface for rear and front wheels respectively. The prediction of traction test result from
existing method and test data, it was found that test data from drawbar pull match with
Gholkar method and test wheel thrust data match with GeeClough method. Coefficient of
rolling resistance was found higher on the bare surface compared to the grassy surface, it
was higher for 2WD compared to 4WD, and finally wet soil gives a higher value compare
to hard dry soil. Highest value of coefficient of rolling resistance was 0.227 and minimum
value was 0.103. The maximum tractive efficiency peak goes up to 62 % for 4WD on the
grass surface on hard soil, and the minimum peak was 24 % for 2WD on the bare surface
on soft plastic soil. Net traction ratio was higher on the grass surface in soft plastic soil for
the tractor in 2WD and the net traction ratio was more or less the same for the grass and
bare surface on hard dry soil for both 2WD and 4WD. Grass surface increases drawbar pull
force for both 2WD and 4WD tractor operating conditions and also for both wet and dry
soil conditions. Dry soil gives higher drawbar pull force compared to wet soil conditions.
Keywords: Traction, rolling resistance, thrust, soil deformation modulus and coefficient of
rolling resistance