A Field Comparison of the Tractive Performance Of

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FIELD COMPARISON OF THE

TRACTIVE PERFORMANCE OF

TWO- AND FOUR-WHEEL DRIVE

TRACTORS

Presented by: Shweta Singh

Roll no. : 13AG61R07

Department: Agricultural and

food engineering

M. J. DWYER

G. PEARSON

1



OVERVIEW

Introduction

Objective

Experimental procedure

Results and discussion Conclusions

References

2



INTRODUCTION

Initially tractors of relatively low hp were

developed, but this has been increased gradually

upto 100 hp over the years.

At increasing engine horsepower the decision

becomes more important on whether and when a

tractor should be equipped with rear-wheel or four-

wheel drive.

3



CONTINUED

In case of 4 WD tractors:

entire weight of the tractor is utilized as load on the

driven axles

Front wheels compact the soil, reduce the rollingresistance and lead to better transmission of power

by the rear wheels.

4



CONTINUED

P= COT ×

where,P=Drawbar pull

COT = coefficient of traction

= dynamic weight on axles

5



OBJECTIVE

To compare the tractive performance of a two-

wheel drive tractor, a four-wheel drive tractor with

front wheels smaller than rear and with equal-sized

wheels.

6



EXPERIMENTAL PROCEDURE

Three tractors were used in the experiment fitted with

same engine giving 63 KW at the p.t.o:

two-wheel drive

four-wheel drive with equal-sized front and rearwheels

and four-wheel drive with front wheels smaller than

rear.

Three conventional non-reversible ploughs 14 inchwide and a harrow was used.

7



CONTINUED

The p.t.o. power was measured and the power

available at the driving axles was measured by a

D.B. test on concrete after the field work had been

completed.

During the field work the tractors were ballasted to

the weights recommended by the manufacturers.

Ploughing was carried out in twelve different fields

and a drawbar test was made on ploughed ground

to simulate disc harrowing in one field

8



Two wheel

drive

Four wheel drive

Unequal size

wheels

Equal size

wheels

p.t.o power, kW 62 62 62

Front tyre size 7.50-18 11.2-24 16.9-34

Rear tyre size 16.9-34 16.9-34 16.9-34

Front axle weight, kg

Fields l-3

Fields 4-l 2

Field 13

1450

1910

980

1820

2260

1500

3510

3510

2910

Rear axle weight, kg

Fields l-3

Fields 4-12

Field 13

3050

2820

3030

2820

2660

3030

1760

1760

19809

Table 1: TRACTOR DETAILS



10

Field

no.

Soil Moisture

Content %

Plough rersistance

(KN/m²)

Cone penetrometer

resistance (KN/m²)1 Clay 50 80 920

2 Clay 20 70 700

3 Clay 39 110 710

4 Clay 31 90 840

5 Sandy loam N.R. 40 1100

6 Sandy clay loam 21 70 740

7 Clay 21 40 1030

8 sandy clay loam 24 50 1070

9 Sandy clay loam 14 60 690

10 Sandy clay loam 26 N.R. 1030

11 Clay loam 45 120 910

12 Sandy loam 19 60 1080

13 Sandy loam 19 N.R. 320

Table 2 : FIELD DETAILS



Cone penetrometer resistance was measured with

a hand-operated cone penetrometer fitted with a

30º cone of 0.5 in.² base area.

Measurements were made at the soil surface and

at depths of 3, 6 and 9 inches.

In fields 1-12 they were made at ten positions on

the unploughed land.

In field 13 measurements were made at ten

positions on the ploughed land.

11



In fields l-12

No-slip travel distance per revolution of the driving

wheels was measured for unploughed land with the

plough raised.

Measurements under load were made with the

tractors ploughing in the normal way.

The time and distance travelled during 7 revolutions

of the rear wheels was measured for a range of

ploughing depths and gears.

The draught force or D.B. pull was measured by

means of a three-point linkage dynamometer.12



Field

no.

Pull at 20% slip in (KN) Maximum drawbar power(KW)

2wd Unequal

size wheel

Equal size

wheel

2wd Unequal

size wheel

Equal size

wheel

1 30 32 34 43 42 48

2 23 24 31 40 40 44

3 22 30 34 31 39 40

4 21 28 34 35 40 445 24 29 30 41 41 43

6 26 32 36 41 42 43

7 22 26 28 38 41 38

8 21 27 25 37 37 46

9 19 24 27 40 41 38

10 N.R. 23 24 N.R. 38 46

11 21 28 32 29 36 42

12 25 26 29 47 49 47

13 12 16 22 25 34 35

13

Table 3 : PULL AT 20% SLIP AND MAXIMUM DRAWBAR POWER



RESULTS AND DISCUSSION

The average pull at 20% slip of the four-wheel drivetractor with unequal-sized wheels was 17% higherthan that of the two-wheel drive tractor and theaverage pull at 20 % slip of the four-wheel drive

tractor with equal-sized wheels was 33 % higherthan that of the two-wheel drive tractor.

The average maximum drawbar power of the four-wheel drive tractor with unequal-sized wheels was7 % higher than that of the two-wheel drive tractor

and that of the four-wheel drive tractor with equal-sized wheels was 14% higher than that of the two-wheel drive tractor.

14



15

Fig. 1. Var iat ion o f theoret ical maximum rate of plo ug hin g withploug h res is tance



MOBILITY NUMBER

wherec = cone penetrometer resistance,

b = tyre width,

d = tyre diameter

w=load carried by tyre

δ = tyre deflection and

h = tyre section height.16



17

Fig. 2. Relationship between coefficient of traction at 20 % slip and mobilitynumber



18

Fig. 3. Relationship between maximum tractive efficiency andmobility number



19

Fig. 4. Relationship between coefficient of traction at maximum

tractive efficiency and mobility number



20

Fig. 5. Relationship between slip at maximum tractive efficiency andmobility number



CONCLUSIONS

The investigation showed that four-wheel drive

tractor with equal sized wheels is capable of

producing approximately 14% more D.B. power in

the field than a two-wheel drive tractor of similar

power.

Maximum rate of work is generally achieved at a

coefficient of traction of approximately 0.4 and a

slip of approximately 10%.

21



REFERENCES

Osborne, L. E. A f ie ld compar ison of the

performance of two- and four-wheel dr ive and

tracklaying tractors . J. agric. Engng Res., 1971

Dwyer, M. J.; Comely, D. R.; Evernden, D. W.Development of the NIAE handboo k o f agr icu l tura l

tyre performance. 5th Int. Conf. of the I.S.T.V.S.,

Detroit, 1975

Soil penetrom eter. A.S.A.E. recommendation R 313,1968

Scholtz, D. C. A th ree-poin t l ink age dynamometer

for restrained l in kages. J. agric. Engng Res., 196622



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A Field Comparison of the Tractive Performance Of