An instrumented drive axle to measure tire tractive performance

An instrumented drive axle is introduced for a prototype tractor using in field research on tractor and implement performance. This mechanism was developed to determine whether such an instrumented drive axle is practical. The drive axle was equipped with a set of transducers to measure wheel angular velocity, rear axle torque and dynamic weight, as well as tire side forces. Measuring the drawbar pull acting on the tractor provides data for calculating net traction, motion resistance and chassis resistance for each driven wheel.     

Soil displacement beneath an agricultural tractor drive tire

Soil strain transducers were used to determine strain in an initially loose sandy loam soil in a soil bin beneath the centerline of an 18.4R38 radial-ply tractor drive tire operating at 10% travel reduction. The initial depth of the midpoints of the strain transducers beneath the undisturbed soil surface was 220 mm. Strain was determined in the vertical, longitudinal, and lateral directions. Initial lengths of strain transducers were approximately 118 mm for the longitudinal and lateral transducers and 136 mm for the vertical transducer. The tire dynamic load was 25 kN and the inflation pressure was 110 kPa, which was a recommended pressure corresponding to the load. In each of four replications, as the tire approached and passed over the strain transducers, the soil first compressed in the longitudinal direction, then elongated, and then compressed again. The soil was compressed in the vertical direction and elongated in the lateral direction. Mean natural strains of the soil following the tire pass were −0.200 in the vertical direction, +0.127 in the lateral direction, and −0.027 in the longitudinal direction. The mean final volumetric natural strain from the strain transducer data was −0.099, which was only 35% of the mean change in natural volumetric strain calculated from soil core samples, −0.286. This difference likely resulted from the greater length of the lateral strain transducer relative to the 69 mm lateral dimension of the soil cores. The strain transducer data indicated the occurrence of plastic flow in the soil during one of the four replications. These results indicate the complex nature of soil movement beneath a tire during traffic and emphasize a shortcoming of soil bulk density data because soil deformation can occur during plastic flow while soil bulk density remains constant.     

The prediction of tractive performance on soil surfaces

A new approach to the traction prediction equation is described. The proposed equation uses the soil deformation modulus and physical properties of agricultural tyres as parameters. The novel features of this approach include the assumption of a non-linear shear stress distribution and change in the value of soil deformation modulus with the normal stress. A model which suggests a relationship between the contact patch area and the soil deformation modulus is also introduced. The prediction equation was compared with the widely used Wismer and Luth equation and measured data obtained by Wittig. The proposed approach results in an improvement over Wismer and Luth in the prediction of traction and it also involves minimal testing.     

How to calculate the effect of soil conditions on tractive performance

The paper presents an analysis and quantitative evaluation of the effect of soil conditions on tractive performance of off-road wheeled and tracked vehicles. The results of this study indicated that to accurately calculate the tractive performance of a vehicle in a given soil condition, soil properties and parameters and their changes as functions of soil moisture content and density should be taken into account. An effective Tractive Performance Analytical (TPA) model which takes into consideration the effect of soil conditions on tractive performance of the vehicles is developed. The TPA model uses invariant soil parameters that can be given or measured before the calculations by routine methods of classical soil mechanics. Soil parameters can also be obtained by recommended empirical equations using four physical soil parameters measured in the field with hand held instruments without time consuming and costly plate or vehicle tests. The model was validated in different soil conditions and compared with other models used in terramechanics for tractive performance predictions. The paper includes also an analysis of capabilities and limitations of the observed models.     

How to predict soil compaction from agricultural tires

A concept of how to predict soil compaction with regard to agricultural machinery, tires and soil is proposed. This approach should provide criteria for choosing vehicles and tires, as well as for the choice of soil testing equipment. It should be stressed that, till now, the concept has only been tested for a few kinds of soil. Therefore, its application to other soil types has to start with one of the proposed “soil calibration tests”.     

An empirical model for tractive performance of rubber-tracks in agricultural soils

Mathematical models capable of describing the interaction between traction devices and soils have been effective in predicting the performance of off-road vehicles. Such a model capable of predicting the performance of bias-ply tires in agricultural soils was first developed by Brixius [Brixius WW. Traction prediction equations for bias-ply tires. ASAE Paper No. 871622. St. Joseph, MI: ASAE; 1987]. When the soil and vehicle parameters are known, this model uses an iterative procedure to predict the tractive performance of a vehicle including pull, tractive efficiency, and motion resistance. Al-Hamad et al. [Al-Hamad SA, Grisso RD, Zoz FM, Von Bargen K. Tractor performance spreadsheet for radial tires. Comput Electron Agr 1994:10(1):45–62] modified the Brixius equations to predict the performance of radial tires. Zoz and Grisso [Zoz, FM, Grisso RD. Traction and tractor performance. ASAE Distinguished Lecture Series #27. St. Joseph, MI: ASAE; 2003] have demonstrated that the use of spreadsheet templates is more efficient than the original iterative procedure used to predict the performance of 2WD and 4WD/MFWD tractors. As tractors equipped with rubber-tracks are becoming popular, it is important that we have the capability to predict the performance for off-road vehicles equipped with rubber-tracks during agricultural operations. This paper discusses the development of an empirical model to accomplish this goal and its validity by comparing the predicted results with published experimental results.     

Laboratory experimental study of tire tractive performance on soft soil: Towing mode,traction mode,and multi-pass effect

Tire tractive performance, soil behavior under the traffic, and multi-pass effect are among the key topics in the research of vehicle off-road dynamics. As an extension of the study (He et al., 2019a), this paper documents the testing of a tire moving on soft soil in the traction mode or towing mode, with a single pass or multiple passes, and presents the testing results mainly from the aspects of tire tractive performance parameters, soil behavior parameters, and multi-pass effect on these parameters. The influence of tire inflation pressure, initial soil compaction, tire normal load, or the number of passes on the test data has been analyzed; for some of the tests, the analysis was completed statistically. A multi-pass effect phenomenon, different from any phenomenon recorded in the available existing literature, was discovered and related to the ripple formation and soil failure. The research results of this paper can be considered groundwork for tire off-road dynamics and the development of traction controllers for vehicles on soft soil.     

The tractive performance of a wide, low-pressure tyre compared with conventional tractor drive tyres

The NIAE single-wheel test vehicle was used to compare the tractive performance of a 67 × 34.00-25 tyre at 0.34 bar inflation pressure with that of 20.8–38 radial tyre at 0.6 bar inflation pressure and a similar 18.4–34 tyre at 0.8 bar inflation pressure. All tyres had similar tread patterns and were tested at the same vertical load of 2250 kg. The best performance was achieved by the 20.8–38 tyre. There was little difference in performance between the other two tyres. When compared with empirical predictions of performance derived from previous work, the two narrower tyres were found to perform approximately as predicted, but the performance of the wide, low-pressure tyre was considerably worse than predicted. This was thought to be due to bulldozing, because of the great width and increased wheel-slip caused by deformation of the soft side-wall and also due to the relatively short ground contact area. It was concluded that wide, low-pressure tyres are only suitable for fitting to vehicles requiring a very low draught capability.     

Measuring soil compaction and soil behavior under the tractor tire using strain transducer

Soil compaction can occur due to machine traffic and is an indicator of soil physical structure degradation. For this study 3 strain transducers with a maximum displacement of 5 cm were used to measure soil compaction under the rear tire of MF285 tractor. In first series of experiments, the effect of tractor traffic was investigated using displacement transducers and cylindrical cores. For the second series, only strain transducers were used to evaluate the effect of moisture levels of 11%, 16% and 22%, tractor velocities of 1, 3 and 5 km/h, and three depths of 20, 30 and 40 cm on soil compaction, and soil behavior during the compaction process was investigated. Results showed that no significant difference was found between the two methods of measuring the bulk density. The three main factors were significant on soil compaction at a probability level of 1%. The mutual binary effect of moisture and depth was significant at 1%, and the interaction of moisture, velocity, and depth were significant at 5%. The soil was compressed in the vertical direction and elongated in the lateral direction. In the longitudinal direction, the soil was initially compressed by the approaching tractor, then elongated, and ultimately compressed again.     

Development of a vehicle to study the tractive performance of integrated steering-drive systems

This paper describes a test-bed vehicle for studying the integration of the steering system of a wheeled vehicle with the drive system. The vehicle was produced in order to determine whether such an integrated system is practical; to investigate tractive performance compared to other steering-drive systems; and to determine under which conditions such a system has better performance. The integrated steering-drive system of the test-bed vehicle uses a computer to co-ordinate the independently driven wheel speeds of the drive system (which is also the primary steering system) with the steer angles of the non-driven steerable wheels to produce a beneficial secondary steering effect. The secondary steering system assists the primary steering system when side forces act on the vehicle, while producing minimal conflict. This concept can be applied to agricultural vehicles such as tractors, harvesters, mowers, sprayers and self-propelled windrowers. The test-bed vehicle is able to be configured for the following steering-drive systems types: open differential drive with steerable wheels, independent drive wheels with castors, locked differential drive with steerable wheels and a computer integrated steering-drive system. The capacity of the test-bed vehicle to be configured as described is a significant advantage when measuring tractive performance, as the results obtained will be more valid due to the vehicle parameters being the same.     

Tire footprint characteristics as a function of soil properties and tire operations

The main objective of the following presentation is to examine the possibility of predicting agricultural tire footprint parameters under different operational conditions. The experimental part of the research involved the operation of two agricultural transport tires on two soils, under variations of tire load, inflation pressures and soil moisture contents. Results obtained show that tire footprint parameters, such as contact area, length, width and sinkage, can be reliably predicted using multifactorial linear and total regressions, within the range of recommended tire loads, inflation pressures and soil moisture contents around the plastic limit.     

Dynamic load distribution and tractive performance of a model tractor

The effect of dynamic load distribution on the tractive efficiency, torque ratio, traction ratio and power distribution of a scaled model tractor was studied under two different soil conditions. The effects of the interactions of dynamic load distribution with slip and total dynamic load were investigated. A relationship between tractive coefficients and dynamic load distribution ratio was proposed.     

Effect of inflation pressure on tractive performance of bias-ply tires

This study was to investigate the effect of inflation pressure on the tractive performance of bias-ply tires for agricultural tractors. Traction tests were conducted at velocities of 3, 4, and 5.5 km h⁻¹ under four different surface conditions using a 13.6–28 6PR bias-ply tire as driving the wheel of the test tractor. When the inflation pressure was reduced from 250 to 40 kPa by a decrement of either 30 or 50 kPa depending upon the test surfaces, some of the test results showed that the traction coefficient and tractive efficiency were increased maximally by 14 and 6%, respectively, at 20% slip. However, such improvements in traction were not statistically consistent enough to find any rules regarding the effect of inflation pressure of bias ply tires on the tractive performance of tractors.     

Prediction of the tractive performance of a flexible tracked vehicle

In this study, we describe a mathematical model designed to allow for the determination of the mechanical relationship existing between soil characteristics and the primary design factors of a tracked vehicle, and to predict the tractive performance of this tracked vehicle on soft terrain. On the basis of the mathematical model, a computer simulation program (Tractive Performance Prediction Model for Tracked Vehicles; TPPMTV) was developed in this study. This model took into account the characteristics of the terrain, including the pressure-sinkage, the shearing characteristics, and the response to the repetitive loading, as well as the primary design parameters of the tracked vehicle. The efficacy of the developed model was then confirmed via comparison of the drawbar pulls of tracked vehicles predicted using the simulation program TPPMTV, with those determined as the result of traction tests. The results indicated that the predicted drawbar pulls, with the change in slip, were quite consistent with the ones measured in the traction test, for the changes in the weight of the vehicle, the initial track tension, and the number of roadwheels within the entire slip range. Thus, we concluded that the simulation program developed in this study, named TPPMTV, proved useful in the prediction of the tractive performance of a tracked vehicle, and that this system might be applicable to the design of a vehicle, possibly enabling a significant improvement in its functions.     

Measurement of soil parameters useful in predicting tractive ability of off-road vehicles using an instrumented portable device

An instrumented portable device that measures soil sinkage, shear, and frictional parameters in situ was developed to investigate the complexity of soil-traction device interaction process. The device was tested to determine its ability to measure soil frictional and shear characteristics. Extensive laboratory tests were conducted using dry and moist Capay clay and Yolo loam soils. In addition, field tests were also conducted in a Yolo loam field located at the UC Davis Agricultural Experiment Station. The Cohron sheargraph was also tested under the same laboratory experimental conditions to determine adhesion, soil-metal friction, cohesion, and angle of internal friction of soil. The analysis of experimental data indicated that soil adhesion and soil-metal friction were found to be functions of the intercept and slope values of cone torque versus cone index plot (r² = 0.94 and 0.95, respectively). Moreover, soil cohesion was found to be related to adhesion by the constrained adhesion relationship, and soil angle of internal friction was proportional to soil-metal friction as reported by Hettiaratchi [7] and [8]. These results imply that a simpler device consisting of a rotating cone can be developed to measure soil frictional and shear characteristics. Preliminary results showed that the soil parameters determined using this device predicted the maximum net traction developed by four different radial ply tires tested by Upadhyaya et al. [18] under similar soil conditions quite well. These results indicate that the parameters obtained from the device could be useful in obtaining traction related parameters of a soil-tractive device interaction process.     

An in-situ determination of virgin compression line parameters for predicting soil displacement resulting from agricultural tire passes

This paper demonstrates the determination of the virgin compression line parameters from initial soil density, contact pressure and resulting rut depth in uniform soil conditions for which a constant soil density change to a depth of 500 mm was obtained in soil bin experiments (whereby total soil depth was 750 mm). The density change was determined with a “non-invasive” technique determining soil displacement (strain) by placing talcum powder lines into the soil during preparation of the soil bin and measuring the change in their relative position. The soil compaction model COMPSOIL with these parameters predicted wheel rut depth to within ±5%, from which in turn an absolute soil density increase can be determined to within ±3%. The model was successfully validated against data for uniform initial densities of 1.2 g/cm³ and 1.6 g/cm³ and a simulated layered field condition. The estimation of the virgin compression line was validated in the field as well. The parameters of the virgin compression line were estimated using soil density change data for the corresponding average contact pressures of different tires with loads of 4.5–10.5 t.     

Finite element modeling of tire/terrain interaction: Application to predicting soil compaction and tire mobility

Tire/terrain interaction has been an important research topic in terramechanics. For off-road vehicle design, good tire mobility and little compaction on terrain are always strongly desired. These two issues were always investigated based on empirical approaches or testing methods. Finite element modeling of tire/terrain interaction seems a good approach, but the capability of the finite element has not well demonstrated. In this paper, the fundamental formulations on modeling soil compaction and tire mobility issues are further introduced. The Drucker-Prager/Cap model implemented in ABAQUS is used to model the soil compaction. A user subroutine for finite strain hyperelasticity model is developed to model nearly incompressible rubber material for tire. In order to predict transient spatial density, large deformation finite element formulation is used to capture the configuration change, which combines with soil elastoplastic model to calculate the transient spatial density due to tire compaction on terrain. Representative simulations are provided to demonstrate how the tire/terrain interaction model can be used to predict soil compaction and tire mobility in the field of terramechanics.     

Demonstration of a portable device for predicting vehicle tractive performance in snow

This workshop study program which was sponsored by the ISTVS Snow Mechanics Committee examined the problems of snow traction and methods of predicting vehicle mobility on snow. This study presents one aspect of the field prediction problem where a portable, hand-held instruments is used and prescribed by requirements for simplicity, portability and facility.