1. Off-Road Equipment Management TSM 262: Spring 2016
LECTURE 6: Tractor Performance III
Off-Road Equipment Engineering
Dept of Agricultural and Biological Engineering

2. Homework and Lab

3. Class Objectives Students should be able to:
Calculate the draft force and drawbar power for an implement
Understand the scope and meaning of the information provided in a Nebraska tractor test report

4. Draft Force for Implements
ASAE D Section 4
Draft data reported as force in horizontal direction of travel
Functional draft (soil and crop resistance) and draft required to overcome rolling resistance of implement included (one exception)
Draft for implements operating at shallow depths is primarily function of implement width and speed
Draft for tillage tools operating at greater depths also dependent on soil texture, depth and geometry of tool

5. Calculation of Draft Force
D=Implement draft, N
F=dimensionless soil texture adjustment (table 1 ASAE D497.7)
i=1 for fine, 2 for medium, 3 for coarse textured soils
A, B, and C= machine-specific parameters
S=field speed, km/h
W=Machine width, m or number of rows or tools
T=Tillage depth, cm, 1 for minor tillage tools and seeding implements

6. Calculation of Draft Force
A, B, C function of tillage tool design
A – function of soil strength
B and C – related to soil bulk density
Soil categories
Fine – high in clay content
Medium – loamy soils
Coarse – sandy soils
Note: expected range of variation (±%) given in table 1 D497.7 due to differences in machine design, machine adjustment, machine age, and site-specific conditions including soil moisture and residue cover

7. Calculation of Drawbar Power
Power = Force x velocity
Pdb = (D x v)/3.6
D=implement draft, kN
v = travel speed, km/h (refer to Table 3, D497.7)

8. Class Problem
A farmer is using a field cultivator for secondary tillage in a loamy soil. The number of tools is 72, the travel speed is 12 km/h, and the tillage depth is 5 cm. Estimate
Implement draft
Drawbar power
Equivalent PTO power from the MFWD tractor

9. Class Problem-Solution
Implement Draft
Drawbar Power

10. Class Problem - Solution
Equivalent PTO power for MFWD tractor

11. Tractor Performance
Where can we find information about tractor performance?
Nebraska tractor test reports
Refer to example

12. What is in a Nebraska test report ?
PTO performance
Max power and fuel consumption
Drawbar performance
Ballasted
Unballasted
Tractor sound level in cab and bystander in high gear
Three point hitch performance / Hydraulic power performance
Hitch dimensions
Reports in English and SI units
Picture of the test tractor
N, rev/min
Pb, kW
Max. power
Gov. max
(rated)

13. Machine data + test conditions
Test location and date
Tractor manufacturer
Fuel, Oil and operating duration
Engine specs
Engine operating parameters
Chassis
Repairs and adjustments
Notes and remarks

14. Use of Nebraska test data
PTO test direct usable power (~90% engine power)
Weather conditions can give 8% change
Drawbar tests on concrete, horizontal for fair comparison among tractors
How to translate that to a soil condition, integral/semi-mounted/towed implement ?

15. Drawbar Tests in Selected Gears
How do they control drawbar load during a test?

16. Basic Tire Design Tire Size 34.00 - R25, 8 Ply Rating Nominal Section
Width, bni
Nominal Rim
Diameter, dnri
Radial

17. Tire Specification: JD 9620
Tire Pressure
psi
Six 480/80R46;***;12(85)
Tire Pressure
kPa
No. of Tires
Radial
Nominal Section
Width, mm
Aspect Ratio
Ht/width %
Nominal Rim
Diameter, in
Index of
Radial tire strength

18. Tire Construction Bias ply – diagonal belts
Radial ply – belts go straight across
Belts included to provide increased rigidity for better tread life

19. Class Exercise