Tire and soil effects on power loss: Measurement and comparison with finite element model results

In the present study, the effect of vertical load, tire inflation pressure and soil moisture content on power loss in tire under controlled soil bin conditions were investigated. Also a finite element model of tire-soil interaction in order to achieve a suitable model for predicting power loss in tire was created. Increasing the vertical load on the tire had a noteworthy impact on increasing the tire contact volume with the soil, reducing the percentage of slip, and increasing the rolling resistance; although, reducing the load on the tire had the opposite effect. At a constant inflation pressure, by increasing the vertical load on the tire, the amount of power loss due to the rolling resistance and the total power loss in the tire increased. Increase in soil moisture content increased the power loss caused by slip. Increasing the inflation pressure at a constant vertical load, also increasing the soil moisture content, led to an increase in the power loss caused by rolling resistance, and increase total power loss. The obtained error for estimating power loss of rolling resistance and total power loss was satisfactory and confirmed the acceptability of the model for power loss estimation.     

The determination of deflection and contact characteristics of a pneumatic tire on a rigid surface

The contact pressure, contact area, contact width, contact length and vertical deflection of a pneumatic tire on a rigid surface depend on tire size, load and inflation pressure and can be derived by means of mathematical expressions. These expressions have been widely utilized and checked in practice for different tires.     

Measurement of contact area, contact pressure and compaction under tires in soft soil

This paper reports about measurements of the contact area of agricultuural tires in a soil bin. Four tires of the dimensions 12.5/80-18, 13.6–28, 16.9–34 and 16.9–26 were tested on a soft sandy loam. Because the existing models for predicting the footprint are complicated, a simplified model has been established, yielding good results. Measured different contact areas of all four tires are nearly constant related to wheel load except for a small increase at higher loads. Using rated loads and applying the appropriate inflation pressure, the ground pressure of a group of similar tires in loose sandy loam is independent of the tire dimensions. Measured soil compaction under at tire a various wheel loads is compared with results obtained by a mathematical model.     

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.     

Soil compaction and tires for harvesting and transporting sugarcane

Four tire types (A, block-shape tread; B, rib-shape tread; C, low-lug tread; D, high-lug tread) used to harvest and transport sugarcane were compared regarding the compaction induced to the soil. Tires were tested at three inflation pressures (207, 276, 345 kPa) and six loads ranging from 20 to 60 kN/tire. Track impressions were traced, and 576 areas were measured to find equations relating inflation pressure, load, contact surface and pressure. Contact surface increased with increasing load and decreasing inflation pressure; however, the contact pressure presented no defined pattern of variation, with tire types A and B generating lower contact pressure. The vertical stresses under the tires were measured and simulated with sensors and software developed at the Colombian Sugarcane Research Center (Cenicaña). Sensors were placed at 10, 30, 50 and 70 cm depth. Tire types A and B registered vertical stresses below 250 kPa at the surface. These two tires were better options to reduce soil compaction. The equations characterizing the tires were introduced into a program to simulate the vertical stress. Simulated and measured stresses were adjusted in an 87–92% range. Results indicate a good correlation between the tire equations, the vertical stress simulation and the vertical stress measurement.     

Tractor tire aspect ratio effects on soil bulk density and cone index

A 580/70R38 tractor drive tire with an aspect ratio of 0.756 and a 650/75R32 tire with an aspect ratio of 0.804 were operated at two dynamic loads and two inflation pressures on a sandy loam and a clay loam with loose soil above a hardpan. Soil bulk density and cone index were measured just above the hardpan beneath the centerline and edge of the tires. The bulk densities were essentially equal for the two tires and cone indices were also essentially equal for the two tires. Soil bulk density and cone index increased with increasing dynamic load at constant inflation pressure, and with increasing inflation pressure at constant dynamic load. In comparisons of the centerline and edge locations, soil bulk density and cone index were significantly less beneath the edge than beneath the centerline of the tires. Soil compaction is not likely to be affected by the aspect ratio of radial-ply tractor drive tires when aspect ratios are between 0.75 and 0.80.     

Tire tread pattern design trigger on the stress distribution over rigid surfaces and soil compaction

Studies comparing the structural differences of tires have not qualitatively or quantitatively considered the effects of tread geometry on tire behaviour or the interactions of the tire with the surface. Therefore, to determine the effects of different tire tread patterns on the stress distribution of the tire and soil compaction, we compared the structural behaviours of a high-flotation tractive-tread (TT) tire and a smooth-tread (ST) tire. The experiments were conducted over a rigid and over a deformable surface. The results from the rigid surface shows the influences of the tread pattern and sidewalls is dependent of the loads. Over the deformable surface, the contact area of the TT tire was larger than that of the ST tire. The inflation pressure (IP) was mainly responsible for the load support before the soil reached its maximum deformation. Next, the tread and sidewalls exhibited the same behaviour as observed on the rigid surface. In addition, we observed alterations in the balloon point with the tread geometry and the type of surface due to changes in the contact pressure. With carcass deformation, the volume of the tire was visibly reduced, which indicated that the IP could increase.     

The effect of inflation pressure and vehicle loading on the sidewall of a radial tire

The sidewall is one of the regions where service failures occur in a pneumatic tire. Knowledge of the stresses or strains developed in the sidewall under varying service conditions is required if such pneumatic-tire failures are to be avoided. This paper describes an experimental investigation into the effect of inflation pressure, vehicle load and camber angle on the sidewall-surface strains in a radial tire. Photoelastic coating and a specially designed strain-gaging technique were used. For pure-inflation pressure, the magnitude of the measured shear strains in the sidewall is directly related to the inflation pressure. The maximum sidewall shear strains in pure inflation are located in the lower sidewall (18 mm from bead), irrespective of the magnitude of the inflation pressure. The mendional sidewall strain is predominant in the inflated but otherwise unloaded tire. The meridional strain is proportional to the square root of the inflation pressure. The maximum mendional strain is located in the mid-sidewall region. For a constant vehicle loading, there is a transition inflation pressure below or above which the circumterential shoulder strain increases sharply. This observation highlights the importance of maintaining satistactory inflation pressure in passenger-car tires as an under-inflated tire will induce severe strain development at the shoulder. In addition to the vehicle load, the introduction of camber angle produces localized change in the meridional and circumterential strains within the contact zone. The increase of camber angle up to 10 deg causes continuous increase in the meridional strain in the lower sidewall but decrease in the upper sidewall. The mid-sidewall meridional strains remain practically unchanged. The circumferential strains along the load line are, in general, lower due to the increase in camber angle.     

Rolling deformation of truck tires: Measurement and analysis using a tire sensing approach

Measurements on rolling tire deformation provide deep insights into the mechanism of generating tire forces and moments. For free rolling tires, substantial attention has been given to the rolling resistance because of its significant impact on the fuel consumption and CO₂ emissions. This paper attempts to investigate the rolling resistance force through measurements of the rolling deformation of truck tires using a tire sensing approach. An optical tire sensor system is used to measure rolling tire deformation, which includes the deformed inner profile, sidewall deformation, and tread deformation. Measurements were conducted on a test truck for both new and used tires. In addition, the influences from operational factors such as wheel load and inflation pressure on tread deformation were examined and analyzed.     

Dynamic load and inflation pressure effects on contact pressures of a forestry forwarder tire

A Trelleborg Twin 421 Mark II 600/55-26.5 steel-reinforced bias-ply forwarder drive tire at inflation pressures of 100 and 240 kPa and dynamic loads of 23.9 and 40 kN was used at 5% travel reduction on a firm clay soil. Effects of dynamic load and inflation pressure on soil–tire contact pressures were determined using six pressure transducers mounted on the tire tread. Three were mounted on the face of a lug and three at corresponding locations on the undertread. Contact angles increased with decreases in inflation pressure and increases in dynamic load. Contact pressures on a lug at the edge of the tire increased as dynamic load increased. Mean and peak pressures on the undertread generally were less than those on a lug. The peak pressures on a lug occurred forward of the axle in nearly all combinations of dynamic load, inflation pressure, and pressure sensor location, and peak pressures on the undertread occurred to the rear of the axle in most of the combinations. Ratios of the peak contact pressure to the inflation pressure ranged from 0 at the edge of the undertread for three combinations of dynamic load and inflation pressure to 8.39 for the pressure sensor on a lug, near the tire centerline, when the tire was underinflated. At constant dynamic load, net traction and tractive efficiency decreased as inflation pressure increased.     

冰面上轮胎摩擦牵引力的实验研究

研制开发了测试冰雪面轮胎力学特性的试验装置,该装置具有可作往复运动的平台冰槽。在不同冰基体温度下,分析了轮胎摩擦引力受侧偏角,载荷和轮胎充气压力的影响,从试验角度论证了轮胎中央充放气系统对改善冬季轮胎牵引性能的作用,该装置的建立将有利于轮胎新结构和新材料的开发,并起到完善现有轮胎力学模型的作用。     

Agricultural tire deformation in the 2D case by finite element methods

The mechanical characteristics of the rubber tire and the interaction between a tire and a rigid surface were investigated by a two-dimensional (2D) finite element (FE) model. The FE model consists of a rigid rim and a rigid contact surface which interact with the elastic tire. Four distinct sets of elastic parameters are used to represent beads, sidewall, tread and lugs. Several sets of tire loads and inflation pressures were applied to the FE model as boundary conditions, together with various displacements and friction conditions. The deformation of the tire profile, the tire displacements in the vertical and lateral directions, the normal contact pressures, the frictional forces and the stress distribution of the tire components were investigated by the 2D FE model under the above boundary conditions. The calculated tire deflections were compared with the measured data. The results show a good fit between calculated and measured data, especially at high load and inflation pressure. The comparison shows that the FE analysis is suitable to predict aspects of the tire performance like its deflection and interactions with the contact surface. Compared with the experimental methods, the FE methods show many advantages in the prediction of tire deformation, contact pressure and stress distribution.     

Tire-ice model development for the simulation of rubber compounds effect on tire performance

The material properties of the rubber compounds, which are highly dependent on temperature, have a vital role in the tire behavior. A comprehensive study on the effect of the rubber properties on tire performance, for different temperatures, as well as different road conditions is required to adequately predict the performance of tires on ice.In this study, a theoretical model has been developed for the tire-ice interaction. The temperature changes obtained from the model are used to calculate the height of the water film created by the heat generated due to the friction force. Next, the viscous friction coefficient at the contact patch is obtained. By using the thermal balance equation at the contact patch, the dry friction is obtained. Knowing the friction coefficients for the dry and wet regions, the equivalent friction coefficient is calculated. The model has been validated using experimental results for three similar tires with different rubber compounds properties. The model developed can be used to predict the temperature changes at the contact patch, the tire friction force, the areas of wet and dry regions, the height of the water film for different ice temperatures, different normal load, etc.     

Steering forces on undriven tractor wheel

The steering forces on an undriven, angled wheel mounting a 6-16 8PR tire were measured on a wheel test carriage at zero camber angle and at 1.5 km/h forward speed in a soil bin with sandy clay loam soil. The lateral force developed was found to be a function of slip angle, normal load, and inflation pressure for a particular soil condition. An exponential relationship could estimate the coefficient of lateral force of the 6-16 tire. The coefficients of this equation were found to be linearly related to inflation pressure. Rolling resistance of the wheel tested was found to be a function of slip angle, normal load, and inflation pressure for the soil condition tested. A linear relationship existed between the rolling resistance and slip angle, where the coefficients were found to be a function of inflation pressure and normal load. The generalized equations developed in the present study for estimating coefficients of lateral force and rolling resistance by taking both the tire and operating parameters into account, were found to be reasonably good by looking at the high coefficient of determination between experimental and estimated values.     

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.     

On the dynamic behavior of agricultural tires

The dynamic behavior of vehicles which are equipped with pneumatic tires depends, to a degree, on the properties of the tire. Therefore, road handling and comfort are also affected by tire characteristics. When the inflation pressure is reduced one obtains a softer “spring”. The dynamic spring coefficient C_dyn increases with increasing rolling speed. Damping coefficient k is related to the excitation frequency by a power function. This function shows a sharp negative slope for low velocities. These conclusions apply to the tire types and test conditions described in this paper.     

Tire load rating to reduce soil compaction

Both experience and research warn that heavily loaded wheels of agricultural transport vehicles and heavy machinery may cause severe compaction damage to the farmland. A remedy consists of reducing both the wheel load and the contact pressure.Early in the 1990s, the author suggested an experimental examination of the problem of soil compaction under fully controlled conditions. The ensuing research program, which was sponsored by the Grant Agency of the Czech Republic, included a series of experiments with loaded wheels carried out in the experimental grounds of the Czech University of Agriculture and, subsequently, their physical modelling in the laboratory of the Department of Motor Vehicles, Technical faculty. This program has corroborated the idea that physical modelling under controlled conditions, complemented by an adequate evaluation procedure, has a promising potential to predict full-scale ground compaction and become a sound basis for practical measures. This paper describes the laboratory equipment, testing technique, and the way of evaluating the compaction potential of tires in terms of soil dry bulk density, leading to a Compaction Number (CN) rating of individual tires. Practically, the CN rating is supposed to be included in agricultural tire catalogues to complement the load capacity/inflation pressure values for hard ground (e.g., ETRTO specifications based on tire strength and wear).     

Effects of tire inflation pressure and tractor velocity on dynamic wheel load and rear axle vibrations

The objective of this study was to evaluate the effects of agricultural tire characteristics on variations of wheel load and vibrations transmitted from the ground to the tractor rear axle. The experiments were conducted on an asphalt road and a sandy loam field using a two-wheel-drive self-propelled farm tractor at different combinations of tractor forward speeds of approximately 0.6, 1.6 and 2.6 m/s, and tire inflation pressures of 330 and 80 kPa. During experiments, the vertical wheel load of the left and right rear wheels, and the roll, bounce and pitch accelerations of the rear axle center were measured using strain-gage-based transducers and a triaxial accelerometer. The wavelet and Fourier analyses were applied to measured data in order to investigate the effects of self-excitations due to non-uniformity and lugs of tires on the wheel-load fluctuation and rear axle vibrations. Values for the root-mean-square (RMS) wheel loads and accelerations were not strictly proportional and inversely proportional to the forward speed and tire pressure respectively. The time histories and frequency compositions of synthesized data have shown that tire non-uniformity and tire lugs significantly excited the wheel load and accelerations at their natural frequencies and harmonics. These effects were strongly affected by the forward speed, tire pressure and ground deformation.     

Finite element modeling of interfacial forces and contact stresses of pneumatic tire on fresh snow for combined longitudinal and lateral slips

Significant challenges exist in the prediction of interaction forces generated from the interface between pneumatic tires and snow-covered terrains due to the highly non-linear nature of the properties of flexible tires, deformable snow cover and the contact mechanics at the interface of tire and snow. Operational conditions of tire-snow interaction are affected by many factors, especially interfacial slips, including longitudinal slip during braking or driving, lateral slip (slip angle) due to turning, and combined slip (longitudinal and lateral slips) due to brake-and-turn and drive-and-turn maneuvers, normal load applied on the wheel, friction coefficient at the interface and snow depth. This paper presents comprehensive three-dimensional finite element simulations of tire-snow interaction for low-strength snow under the full-range of controlled longitudinal and lateral slips for three vertical loads to gain significant mechanistic insight. The pneumatic tire was modeled using elastic, viscoelastic and hyperelastic material models; the snow was modeled using the modified Drucker-Prager Cap material model (MDPC). The traction, motion resistance, drawbar pull, tire sinkage, tire deflection, snow density, contact pressure and contact shear stresses were obtained as a function of longitudinal slip and lateral slip. Wheel states - braked, towed, driven, self-propelled, and driving - have been identified and serve as key classifiers of discernable patterns in tire-snow interaction such as zones of contact shear stresses. The predicted results can be applied to analytical deterministic and stochastic modeling of tire-snow interaction.     

Tire-soil interaction model for turning (steered) tires

A review of the experimental information on the development of lateral forces on tires traveling at an angle to their center plane is presented and the usefulness of the consideration of the lateral forces for the development of an analytical model is evaluated. Major components of the lateral force have been identified as the forces required to balance the tractive force and the drawbar pull vectorially. The lateral forces are generated by the shear stresses developing in the contact area and the horizontal component of the normal stresses acting on the in-ground portion of the curved side walls of the tire. The tire-soil interaction model for steady state straight travel has been expanded to include the necessary algorithms for the calculation of these lateral forces. The pattern of tractive force-slip and longitudinal-lateral force relationships is in general agreement with experiments.