ASeminar

on

STEERING FORCES ON UNDRIVEN, ANGLED WHEELS

Author: Gee-Clough & M. S. Somme

Speaker:Ravikant Sainath GhotekarM.Tech (1st year), FMP, AGFE,IIT Kharagpur

CONTENT

Introduction

Dimensional analysis

Experimental procedure

Results

Modelling of the results

Conclusions

References

INTRODUCTION• Measurements of the soil forces acting on a driven or undriven

are required for two main purposes:

1) To investigate stability both when working on levelground and on side-slopes

2) To investigate handling characteristics

• Only three attempts have been made to model these forces

Taylor and Birtwhistle

Schwanghart

Krick

• With the exception of Schwanghart's model, none of thesemodels is sufficiently general to be of widespread use.

Contd…

• So requirement is a model of the tyre-soil interaction which will allow the forces on a steered wheel to be readily predicted from a knowledge of the wheel parameters and soil condition.

DIMENSIONAL ANALYSISParameters required to describe the system

18 parameters --- 15 non-dimensional groups

Freitag:Analysis contd…

Turnage:Analysis contd…

EXPERIMENTAL PROCEDURE• Research done at the Deere Technical Centre, Moline, Illinois

Experimental procedure contd…

• All runs were carried out at a forward speed of 0.5 m/s

• The soil used contained 43.8% sand, 34.2 % silt and 22.0 % claywhich is a loam soil & Moisture content was 12%

• soil was processed by cultivating blades, a scraper and roller

• Measurement of the cone penetrometer resistance was madefor every soil sample

• the aligning torque was extremely small so it was taken to bezero

Experimental procedure contd…

RESULTSCoefficient of rolling resistance at zero slip angle

Results cont…The effect of tyre size, load and inflation pressure at constant slip angle

Results cont…The effect of slip angle at constant load

The effect of slip angle at constant load in different soil conditions

Results cont…

The effect of "bulldozing" in very soft soilsResults cont…

The effect of load and inflation pressure at varying slip angles in the same soil

Results cont…

Fig. 8: Coefficient of side force at 10 ° slip angle against the four different mobility numbers

MODELLING OF THE RESULTS

Fig. 8: Coefficient of side force at 10 ° slip angle against the four different mobility numbers

Modelling cont…

Fig. 9: Measured values of (CRR)w plotted against the four versions of mobility number

Modelling cont…

Fig. 9: Measured values of (CRR)w plotted against the four versions of mobility number

Modelling cont…

• Requirements for modelling:

a. The effects of slip angle, tyre size, load, inflation pressure and soil condition on the tyre side force were all able to be predicted satisfactorily using the tyre mobility number and the relationship.

b. The effect of these parameters on tyre rolling resistance was not predicted so satisfactorily, particularly at high values of slip angle and mobility number.

c. information on tyre steering forces will be for stability and handling calculations.

Modelling cont…

Modelling cont…

Modelling cont…

Modelling cont…

Relationship between (Csf)w

/(CRR)w and mobility number

Modelling cont…

Modelling cont…

Modelling cont…

Modelling cont…

CONCLUSIONS• For zero camber angle and low speed, the dimensional analysis

indicated that the performance parameters should be functions oftyre mobility number, soil internal friction angle and slip angle.

• The wheel aligning torque was negligibly small in all the experiments.

• The coefficient of side force relative to the wheel, (Csf)w, was relatedto the slip angle α, by an exponential relationship of the form

in all the experiments except that in the weakest soil (cone indexvalue150 kPa)

• The coefficient of rolling resistance relative to the wheel, (CaR)w, wasan irregular function of α. However, a linear relationship was foundbetween (CRR) w and α at slip angles between 0 and 20°.

• (Csf) w at a slip angle of 10 ° could be adequately modelled using themobility numbers EMOB and AMOB so long as soil cone index valuewas a measure of soil cohesion and soil internal friction. The mobilitynumber φMOB, using both cohesion and internal friction angle, gavethe best correlation with (Csf)w. angle did not vary.

• (CRR)w at a slip angle of 10 ° was modelled equally well by all fourversions of mobility number.

• As mobility number increased the ratio (Csv)w/(CRR) w alsoincreased and for slip angles greater than 20 °, (CsF)w was always atleast 5 times as large as (CRR) w.

• The product k{(Csf)w}max increased as mobility number increasedand a statistically significant relationship was established.

Conclusions cont…

REFERENCES• D. GF.E-CLOuGH, M. McALLIS'rER, G. PEARSON and D. W.

EVERNDEN, The empirical prediction of tractor-implement fieldperformance, J. Terramechanies 15(2), (1978).

• R. D. WISMER and H. J. Ltrrn, Off-road traction prediction forwheeled vehicles. J. Terramechanics 10(2), (1973).

• G. KNICK, Bchaviour of tyres driven in soft ground with sideslip. J. Terramechanics, 9(4), (1973).

• H. SCHWANGHART, Lateral forces on steered tyres in loose soil.J. Terramechanics 5(1), (1968).

Modelling• Scientific activity the aim of which is to make a

particular part or feature of the world easier to understand, define, quantify, visualize, or simulate

1. Conceptual models

2. Operational Model

3. Mathematical models

4. Graphical models