Grousers Effect in Tracked Vehicle Multibody Dynamics with Deformable Terrain Contact Model

In this work, a multibody model of a small size farming tracked vehicle is shown. Detailed models of each track were coupled with the rigid body model of the vehicle. To describe the interaction between the track and the ground in case of deformable soil, custom defined forces were applied on each link of the track model. Their definition derived from deformable soil mechanics equations implemented with a specifically designed routine within the multibody code. According to the proposed model, it is assumed that the main terrain deformation is concentrated around the vehicle tracks elements. The custom defined forces included also the effects of the track grousers which strongly affect the traction availability for the vehicle. A passive soil failure model was considered to describe the terrain behaviour subjected to the grousers action. A so developed model in a multibody code can investigate vehicle performance and limit operating conditions related to the vehicle and soil characteristics. In this work, particular attention was focused on the results in terms of traction force, slip and sinkage on different types of terrain. Tests performed in the multibody environment show how the proposed model is able to obtain tractive performance similar to equivalent analytical solutions and how the grousers improve the availability of tractive force for certain type of soil characteristics

Special tractor driving wheels with two modification of spikes inclination angle

ArticleThe paper presents a research on an improvement of tractor drawbar properties using special driving wheels. Two modifications of the special driving wheels were designed and tested under field conditions. The results were compared with standard tyres. The special driving wheels consists of the tyres with a modified tyre-tread pattern and equips with the spike segments. The special driving wheels allow to activate or deactivate the spike segments to improve a drawbar pull at worse adhesive conditions of the ground or transport on roads with standard tyres. The first modification activates all 8 spike segments at spike inclination angle 90° and the second one 4 at angle 90°and 4 at 30°. The measurements were realised in October 2017 in an area of the Slovak Agricultural Museum in Nitra. The drawbar properties of the special driving wheels were evaluated based on drawbar pull of the test tractor Mini 070 type connected with a load tractor MT8-065 type. Using the test tractor in 1st and 2nd gear, the measurements were realized at 100% wheels slip and repeated 4 times. The results show the statistically significant differences in the drawbar pull of the test tractor with different driving wheels on a grass plot. The highest increase in drawbar pull reached the value 25.56% (2nd gear) and 19.98% (1st gear) in case of the special driving wheels with 4 spike segments at 90° and 4 at 30°. In case of the special driving wheels with 8 spike segments at 90°, increase in the drawbar pull reached the value 10.09% (1st gear) and 15.21% (2nd gear) in comparation with the standard tyres

Analytical and finite element modelling of the dynamic interaction between off-road tyres and deformable terrains

Automotive tyres are one of the main components of a vehicle and have an extremely complex structure consisting of several types of steel reinforcing layers embedded in hyperelastic rubber materials. They serve to support, drive – accelerate and decelerate – and steer the vehicle, and to reduce transmitted road vibrations. However, driving is associated with certain types of pollution due to CO2 emissions, various particles due to tyre wear, as well as noise. The main source of CO2 emissions is the tyre rolling resistance, which accounts for roughly 30% of the fuel consumed by cars. The phenomenon becomes more pronounced in off-road conditions, where truck vehicles are responsible for about a quarter of the total CO2 emissions. Appropriate legislation has been introduced, to control all of these pollution aspects. Therefore, tyre simulation (especially in off-road conditions) is essential in order to achieve a feasible design of a vehicle, in terms of economy and safety. [Continues.

Traction and Agricultural Tractor Tire Selection Studies.

A machine was built to study non-rolling tire stiffness and damping coefficients of agricultural tractor tires in the vertical direction. Static deflection on a rigid surface was measured as a function of vertical load. During dynamic experiments, a sinusoidal forcing function was imposed on the test tire to determine dynamic stiffness and damping coefficient from load and deflection measurements. The experimental setup and methodology are described. Ten tires were tested. Both static and dynamic stiffnesses appeared linearly related to inflation pressure. No correlation was found between dynamic properties and excitation frequency. Comparisons among stiffness and damping coefficient values were made according to section width, carcass construction, and between tires of the same size. Traction tests were made at the National Soil Dynamics Laboratory, Auburn, Alabama. Four tires (14.9-30, 14.9R30, 18.4-38 and 18.4R38) were tested on Norfolk Sandy Loam after measuring their rolling radius on concrete under self-propelled condition, at three levels of inflation pressure, and under varying load. Traction experiments were made at three levels of inflation pressure, two levels of longitudinal slip (7.5 and 15%) and under varying dynamic load for each tire. Slip, carcass construction and inflation pressure significantly affected the pull ratios. A mathematical model is proposed that accounts for effects of tire inflation pressure and dynamic load on rolling radius

Analysis of Off-Road Tire-Soil Interaction through Analytical and Finite Element Methods

Tire-soil interaction is important for the performance of off-road vehicles and the soil compaction in the agricultural field. With an analytical model, which is integrated in multibody-simulation software, and a Finite Element model, the forces and moments generated on the tire-soil contact patch were studied to analyze the tire performance. Simulations with these two models for different tire operating conditions were performed to evaluate the mechanical behaviors of an excavator tire. For the FE model validation a single wheel tester connected to an excavator arm was designed. Field tests were carried out to examine the tire vertical stiffness, the contact pressure on the tire – hard ground interface, the longitudinal/vertical force and the compaction of the sandy clay from the test field under specified operating conditions. The simulation and experimental results were compared to evaluate the model quality. The Magic Formula was used to fit the curves of longitudinal and lateral forces. A simplified tire-soil interaction model based on the fitted Magic Formula could be established and further applied to the simulation of vehicle-soil interaction.Die Reifen-Boden-Interaktion ist wichtig für die Leistungsfähigkeit von Geländefahrzeugen und die Bodenverdichtung landwirtschaftlicher Nutzflächen. Mit Hilfe einen analytischen Models, das in eine Mehrkörpersimulation Software integriert wird, und der Finite Elemente (FE) Modell, werden die Kräfte und Drehmomente für die Analyse des Reifenverhaltens ermittelt. Es wurden Simulationen bei unterschiedlichen Betriebszuständen eines Baggerreifens durchgeführt und das mechanische Verhalten ausgewertet. Um das FE-Modell zu validieren, wurde ein Einzelrad-Tester entwickelt, welcher an einen Baggerarm angekuppelt wurde. In Feldversuchen wurden die Reifensteifigkeit, die Spannung in der Reifen-Hartboden-Kontaktfläche, sowie die longitudinalen und vertikalen Kräfte und die Verdichtung des Sandigen Lehmbodens in Abhängigkeit von vorgegeben Reifenbetriebszuständen untersucht. Für die Bewertung der Modellqualität werden die Ergebnisse von Simulationen und Experimenten verglichen. Das Magic Formula wurde heraufgezogen, um die Kurven der longitudinalen und queren Kräfte anzupassen. Mittels die Magic-Formula-Funktion wird ein Modell der vereinfachtes Reifen-Boden-Interaktion zur Verfügung steht, mit dem könnte die Fahrzeug-Boden-Interaktion simuliert werden kann

Automated processor for optimizing tractor operation.

Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.The agricultural tractor is designed as a general purpose machine and consequently, does not perform all its tasks at maximum efficiency. Various methods of increasing the field performance of these vehicles have been studied. Traction is one of the main factors limiting the field performance of the modern tractor. The process of developing traction has therefore been investigated by many researchers and although this study has resulted in a better understanding of the mechanics, it has not to any great extent assisted the operator to optimize performance in the field. It was concluded that in order to solve the problem the operator required a control system to maintain the dynamic load and inflation pressure at optimum levels. Work was carried out to develop and evaluate such a system using the Single Wheel Traction Research Vehicle at the USDA's National Soil Dynamics Laboratory in Auburn, Alabama, USA. A computer management system was developed to control the dynamic load, net traction and inflation pressure of the test tyre. During a simulated field operation the system was programmed to cycle the tyre over its operating range of dynamic load and inflation pressure while monitoring tractive efficiency. A tractive efficiency response surface was computed for the particular condition and the surface searched for the dynamic load and inflation pressure levels which resulted in maximum tractive efficiency. The tyre was then controlled and operated at maximum tractive efficiency. Evaluation showed that within the operating range of the tyre, tractive efficiency varied considerably with dynamic load, inflation pressure, net traction and soil condition. The results indicated that a considerable advantage could be obtained by using such an arrangement on a tractor. The system would automatically maximize the tractive efficiency of the tractor under the particular field conditions and with the particular implement being used. Implements could be ballasted and the hitch system used to control the weight transfer to ensure maximum tractive efficiency. Systems such as these would result in a significant improvement in the field performance of the machine and a reduction in management time required to optimize the performance of the tractor implement combination

Tractive performance of 4x4 tyre treads on pure sand.

This thesis examined the difficulties of generating traction from 4x4 (light truck) tyres in pure sand conditions. Investigations conducted in the Cranfield University Soil Dynamics Laboratory measured the tractive performance of a range of production and prototype 4x4 tyre tread patterns to quantify the effect of tread features upon tractive performance. The investigation also quantified the amount of sand displacement instantaneously occurring beneath the tyre, by a novel application of radio frequency identification (RFID) technology, which determined sand displacements to an accuracy of ±5.5 mm. A limited number of normal contact stress measurements were recorded using a TekScan normal pressure mapping system. This technology was employed in a new manner that allowed pressure distributions to be dynamically recorded on a deformable soil surface. Models were developed or adapted to predict rolling resistance, gross thrust of a tyre and the gross thrust effect due to its tread. Net thrust was predicted from refined versions of equations developed by Bekker to predict gross thrust and rolling resistance. These were modified to account for dynamic tractive conditions. A new tread model proposed by the author produced a numerical representation of the gross thrust capability of a tread based on factors hypothesised to influence traction on loose sand. This allowed the development of a relationship between the features of the tread and its measured gross thrust improvement (relative to a plain tread tyre), from which a total relationship was developed. The tread features were also, in combination with the wheel slip, related to the sand displacements and net thrusts simultaneously achieved. The sand displacement results indicated that the majority of the variation in displacement between the different treads occurred in the longitudinal (rearward) direction. This effect was influenced by the wheel slip, as increased slip caused greater displacements, so the differences between the treads were greater at higher slips. The treads that generated the highest relative displacements also derived the higher gross thrusts (up to +5% extra gross thrust compared to a plain tread), although at the higher slips this also caused increased sinkage. As sinkage increased, the rolling resistance increased at a fester rate then the gross thrust, and thus the net thrust reduced. To prevent this effect the wheel slip should be limited to a maximum of 20% at low forward speeds (approximately 5 km/h). Current market forces dictate that the biggest benefit that tyre manufacturers could offer in desert market regions would be to optimise road-biased tyres to suit loose sand conditions. The modelling developed indicated that this could be achieved by maximising the number of lateral grooves (and thus lateral edges) featured on a tread, however care would have to be exercised so as not to compromise the necessaiy on-road capability. The models could also be used to quantifiably determine from a choice of possible tyre treads, the tread that would offer most traction on pure loose sand

The dynamics of towed seeding equipment

Seed depth consistency is a critical performance metric of agricultural seeding equipment. To improve productivity, equipment manufacturers have historically focused on increasing the equipment working width of hoe-opener style seeding drills (hoe drills). However, the physical limitations of hoe drill size do present a design challenge. Increasing seeding speed to improve equipment productivity continues to be a challenge for equipment designers. Most operating conditions restrict hoe-drill seeding speeds to approximately 2.2 m/s (5 mph); depth consistency generally degrades above this speed with current hoe drill technology. This research focused on developing an understanding of why this performance degradation occurs as speed increases. The general industry hypothesis points vaguely to "excessive motion" of the components to which the soil-engaging tools connect (the row units). However, little research on the dynamics of towed agricultural implements was found in the open literature. An understanding of the mechanism(s) causing this "excessive motion" was sought during this research. A 2-D simulation tool was developed in MATLAB to provide equipment designers with the capability to conduct performance trade-off and sensitivity studies early in the prototype stage of a project. The simulation tool was compartmentalized so that changes to equipment geometry, component-soil contact models, or hydraulic systems could be modified with little or no change to other parts of the program. Operational data were also collected using a small plot drill based on a New Holland P2070 Precision Hoe Drill. Data were collected at multiple operating speed up to 4.4 m/s (10 mph) to characterize depth consistency issues present at higher speeds. Various geometric seed depth and hydraulic pressure settings were also tested. Kinematic parameters (acceleration, position), force, hydraulic pressure, and video of the instrumented row unit were recorded during steady-state the operation of the machine in typical seeding conditions. Measured data aided in calibrating aspects of the simulation tool, and the tool enabled certain performance features in the measurement data to be explored further. Frequency domain acceleration power spectra revealed that row unit acceleration power was generally concentrated at two frequencies. The terrain profile of the test field contained furrows from the previous seeding operation; this resulted in acceleration power to be concentrated at a distinct speed-dependent frequency related to the furrow spacing. While somewhat expected, this indicated the general inability of the current design to attenuate terrain inputs. The small packer wheel provided little compliance between the row unit and soil, so improving the attenuation performance of the system could improve depth consistency performance in future designs. The second major acceleration spectra feature was related to the arrangement of the hoe opener and trailing packer wheel; both rigidly connect to the row unit body. The row unit position changed when the packer wheel encountered a terrain bump or dip; this resulted in a change in the vertical position of the hoe opener located in front of the packer wheel. Immediate changes in the operating depth of the hoe opener tool resulted. Also, depth changes generally modified the terrain such that a new bump or dip was created in the soil surface preceding the packer wheel, thus creating a feedback path between the hoe opener and packer wheel. Considering the simplifications of the 2-D model, agreement between simulated and measured data was encouraging. The frequencies of the above phenomena were in reasonable agreement throughout the speed range of interest. Power spectra amplitude differences were likely due to both input terrain differences between simulation and test terrains, and simplifications made in representing soil-tire and soil-tool contact. Future work to improve these sub-models, and to further explore the observed non-linear effect of hydraulic pressure changes would improve the predictive accuracy of the model presented

Advances in Mechanical Systems Dynamics 2020

The fundamentals of mechanical system dynamics were established before the beginning of the industrial era. The 18th century was a very important time for science and was characterized by the development of classical mechanics. This development progressed in the 19th century, and new, important applications related to industrialization were found and studied. The development of computers in the 20th century revolutionized mechanical system dynamics owing to the development of numerical simulation. We are now in the presence of the fourth industrial revolution. Mechanical systems are increasingly integrated with electrical, fluidic, and electronic systems, and the industrial environment has become characterized by the cyber-physical systems of industry 4.0. Within this framework, the status-of-the-art has become represented by integrated mechanical systems and supported by accurate dynamic models able to predict their dynamic behavior. Therefore, mechanical systems dynamics will play a central role in forthcoming years. This Special Issue aims to disseminate the latest research findings and ideas in the field of mechanical systems dynamics, with particular emphasis on novel trends and applications