The lateral stability of tractor and trailer combinations

A model has been developed to predict the lateral stability characteristics of tractor and unbalanced trailer combinations. For present combinations, stability deteriorates with speed culminating in instability at forward speeds in the region of 18 m/s. The effect of tractor and trailer size and other parameter variations on this speed dependent instability are examined.The effect of braking with and without axle locking are analysed. The stability of the combination is sensitive to the braking distribuion between the axles, which affect the hitch forces developed. Locking the tractor rear or trailer axle results in instabilities, commonly termed jack-knifing and trailer swing respectively. Jack-knifing is the more hazardous instability, whereas trailer swing although potentially dangerous has a divergence approximately an order of magnitude less.The potential of the model for predicting lateral dynamic behaviour of design concepts for future high speed farm transport which would operate at higher speeds than the current maximum of 9 m/s for tractor and trailer combinations is discussed. The scope for generalizing the model to examine other aspects of lateral behaviour, such as steering response is restricted by the limited amount of data available on the side force generated by tyres in agricultural conditions.     

Automatic control of a modified tractor to work on steep side slopes

The main purpose of this paper is to investigate the control and stability of a tractor moving over obstacles on steep side slopes. To this end, a modified slope tractor is considered and the lateral stability of the vehicle is studied. The modified tractor is able to roll against the side slope and change the position of its mass centre. The tractor behaviour in a sloped field on a straight path is simulated in ADAMS software environment. A two-layer controller consisting of a Fuzzy upper layer and a PI lower layer is designed for the control of tractor stability. The dynamics of hydraulic actuators adjusting the body roll angle is also included. The stability of controlled and uncontrolled tractors is investigated by several simulations. It is shown that in comparison with the two types of ordinary and uncontrolled slope tractors, the controller is capable of maintaining the stability of modified tractor and preventing it from rollover and instability on various side slopes and obstacles.     

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.     

Effects of tyre inflation pressure and forward speed on vibration of an unsuspended tractor

Relationships among intensity of vibrations, tractor speed, soil moisture content and tyre inflation pressure are important for the design of tractor suspension systems. This study was designed to evaluate the effect of tyre inflation pressure and forward speed on tractor vibration in the paddy fields of Southern China by using a two-wheel-drive unsuspended tractor with different combinations of forward speed, tyre inflation pressure and soil moisture content. During experiments, the vertical vibration accelerations in front and rear axles and triaxial vibration accelerations of the tractor body were measured using three accelerometers. Fourier analysis was applied to determine root mean square acceleration values in the low frequency range from 0.1 to 10 Hz. The results of the study indicate that tractor vibration is strongly affected by changing forward speed and tyre inflation pressure, and especially by changing forward speed and rear tyre inflation pressure. The research also shows the variation in the pattern of vibration intensity especially at the tractor’s front axle when field soil moisture content is changed.     

The determination of plough draught—Part II the measurement and prediction of plough draught for two mouldboard shapes in three soil series

The draught of a 3-furrow reversible plough fitted with two types of bodies was measured at five separate test sites. Each site was ploughed on four different days to provide a range of soil moisture contents. The plough was operated at three different speeds in sequence for each type of body. The horizontal and vertical forces transmitted to the tractor were measured on a three-point linkage dynamometer. Tachogenerators monitored tractor wheel speed and fifth wheel ground speed. Cone index and soil specific weight were recorded at 30 mm intervals throughout the top-soil profile. Cone index at median plough depth was found to be a satisfactory measure of soil strength for the prediction of plough draught. Characterising specific plough draught by soil cone index, specific weight, moisture content, plough mouldboard tail angle and ploughing speed provided predicted values in closer agreement with measured draught compared with earlier equations. The sensitivity of cone index to soil moisture content supports the use of the cone penetrometer as a practical monitor of soil conditions in the field and as a management tool for judging the opportune times for agricultural tillage operations.     

Computerized instrumentation system for monitoring the tractor performance in the field

A high precision computerized instrumentation package was developed and mounted on a 50 kW tractor to monitor and measure various performance parameters of a tractor and implement system. The system was intended to be used for the compilation of a database of draft requirements of tillage implements. The system designed to measure: three-point linkage forces, ground speed, tillage depth, fuel consumption, forward speed, slip, engine speed, hydraulic pressure and fluid temperatures. The data acquisition unit was based on a high speed multi processors Campbell Scientific CR3000 data logger linked to a microcomputer using suitable transducer. The average calibration constants for the rear wheel speed, fuel consumption and three point linkage transducers were 0.0364 m/pulse, 0.000142857 l/pulse and 0.66 mV/kN respectively. The data acquisition system was capable of scanning rate up to 100 K sample/s. Data acquisition system was developed to measure draft of primary tillage implements in vertisol.     

Analysis of shifting performance of power shuttle transmission

This study was conducted to investigate the effects on the shifting performance of the design parameters of a power shuttle tractor using a computer simulation technique. The EASY 5 models of the hydraulic control system and power shuttle transmission were developed, and combined with a tractor model to complete a simulation model for a power shuttle tractor. The models for the hydraulic control system and power shuttle transmission were verified using an experimental power train constructed for the validation purpose.The design parameters included the terminal pressure and time for the modulation of the hydraulic control system, and forward speed, weight, shuttle gear ratio and torsional damping of the tractor. The shift performance was evaluated in term of the peak torques of the input shaft of the transmission and tractor axles, and power transmitted per unit area of the clutch and the time required for the power transmission.     

Dynamic analysis of turning performance of 4WD-4WS tractor on paved road

In this research, using a 4-wheel-driven, 4-wheel-steered tractor, two experiments and a computer simulation about its turning on paved ground are described. One experiment is on the relation between the wheel turning angle and the steering angle, and the other is a turning experiment to determine the path traced by the vehicle and to check the simulation. The computer simulation with equations of motion was conducted, and some effects, for example of the running speed, on the yaw angular velocity and on the side slip angle of the center of gravity of the tested tractor were analysed.     

基于持续同调的边坡土颗粒应力链失稳分析

采用颗粒离散元方法和持续同调理论,研究了内排土场堆叠至不同高度时的边坡稳定性。为便于研究,现采用一水平金属板向下施加压力,代替不同厚度土层的重力荷载,对边坡在竖向荷载作用下的失稳破坏过程进行了颗粒离散元模拟。研究了二维边坡土颗粒速度总矢量、边坡失稳破坏时滑移开裂面的角度以及边坡坡顶y方向的平均速度等宏观响应过程,并构建了自然堆积下边坡堆积体颗粒的法向力链无向网络模型。最后,用持续同调方法对边坡坡顶颗粒接触力链网络的拓扑特征进行分析,获得条码图,建立了岩体结构持续同调特征与失稳演化的关系。本文为研究边坡失稳拓扑识别提供了一种新方法,从而可以有效预测边坡的失稳破坏。     

Speed advice for power efficient drawbar work

Tractor manufacturers already offer engine - transmission control systems in which the operator decides whether low fuel consumption or high output is the priority and let a control system provide engine and transmission management. Less sophisticated tractors, as well as older equipment, still rely on the operator awareness upon what driving parameters most enhance efficiency. The objective of this study is to analyse the effect of driving parameters, namely forward speed and engine speed on the overall power efficiency. The overall power efficiency of a tractor performing drawbar work is the ratio between the output power at the drawbar and the energy equivalent of the fuel consumed per unity of time. Experimental data obtained from tractor field tests in real farm conditions, within the range of 0.2-0.4 for the vehicle traction ratio (ratio of the drawbar pull to the total weight of the tractor), show that increments of 10-20% on the overall power efficiency can be obtained by throttling down from 2200 min⁻¹ to 1750 min⁻¹ (idle speed). The reduction in ground speed and therefore in the work rate, may be overcome by shifting up the transmission ratio.     

Development and implementation of an IOT based instrumentation system for computing performance of a tractor-implement system

A high precision and compact IOT based digital instrumentation setup to measure, display and record various tractor and implement system performance parameters was developed and installed on a 28.3 kW Tractor. The setup was capable of continuous monitoring and wirelessly transmitting tractor-implement performance parameters on a cloud platform such as engine speed, radiator fan speed, fuel consumption, draft, forward speed, lift arm angle, wheel slip, wheel slip, PTO speed, geo-location/position of the tractor, choking of seeds in the implement and vibrations experienced by the implement. For precision measurements, commercial transducers used in the system were calibrated and assessed under both static and dynamic conditions. The average calibration constant for fuel consumption, forward speed, lift arm angle and load cell were 0.00009804 L/pulse, 0.01610306 km/h/pulse, 0.056 mA/degree and 0.2575 mV/kN respectively. The system based on DataTaker DT 85 Data logger connected to a micro-computer through transducers capable of transferring data wirelessly was installed on John Deere 5038 tractor and was tested with a Spatially Modified No-Till Drill in agricultural field with varied implement depth.     

Numerical simulation of a 4WD–4WS tractor turning in a rice field

For the steady-state circular turning of a 4WD–4WS (4 wheel driven–4 wheel steered) tractor in a rice field, a numerical simulation was achieved. Equations of motion of this tractor were developed in a vehicle fixed x–y coordinate system. By comparing the calculated and measured results of acting forces on the tractor tires, this simulation was evaluated. Then, the characteristic parameters of the turning vehicle, which are the side slip angle and the yaw angular velocity of the vehicle center of gravity, were simulated in several combinations of the steering wheel angle and the forward speed. Also the same simulation applied to a 4WD–2WS tractor which had the same body as the 4WD–4WS tractor. The simulated results showed a clear difference of turnability between 4WS and 2WS. ©     

高陡岩质料场边坡稳定性与支护设计研究

水电站料场高边坡具有高度大、坡度陡、卸荷速度快等特点,因多按临时边坡进行设计,故施工期变形破坏事例频发。基于这一现状,依托瀑布沟水电站两岩质料场边坡,通过两年多跟踪施工过程的支护设计工作,总结出一套操作性强的料场高边坡稳定性及支护设计方法。针对料场边坡存在的受软弱结构面控制的边坡整体稳定性、浅表层块体稳定性、碎裂岩体稳定性三种工程地质问题,在跟踪施工过程开展岩体结构调查的基础上,按照先整体后局部的稳定性评价思路,开展高边坡稳定性评价。施工期动态支护设计按照“保证整体稳定,控制局部变形,顾全潜在失稳区域”的理念,通过定性评价确定不稳定区域并优先设计提交施工;针对施工中最易出现的块体变形和碎裂岩体变形,建立了合理的支护设计原则和严格的施工规定;对稳定性差、施工风险高、支护造价大的潜在不稳定区域,应及时地调整开挖方案,减少工程造价。实践表明,这套方法保证了料场高边坡的快速施工安全,减少了工程投资。     

Analysis of the PTO load of a 75 kW agricultural tractor during rotary tillage and baler operation in Korean upland fields

In this paper, the PTO severeness of an agricultural tractor during rotary tillage and baler operation was analyzed. The S–N curves of the PTO driving gears were obtained through fatigue life test. To obtain the S–N curves of the PTO driving gears, the breakage time and rotational speed of the gears were measured through observation of the bending stress with changing torque. The torque acting on the PTO was measured and analyzed during rotary tillage and baler operation. Rotary tillage and baler operation were conducted at two ground speeds and two PTO rotational speeds at upland field sites with similar soil conditions, respectively. The load data were inverted to a load spectrum using rain-flow counting and SWT equations. Modified Miner’s rule was used to calculate the partial damage sum. The severeness was defined as the relative ratio of the damage sum. The results showed that the damage of the PTO increased when the ground speed or the PTO rotational speed increased. The effect of the PTO rotational speed on the severeness of the PTO was more significant than that of the ground speed. The severeness of the PTO of rotary tillage was greater than that of baler operation.     

Influence of the axle load, tyre size and configuration on the compaction of a freshly tilled clayey soil

Enhancement of the potential root growth volume is the main objective of farmers when they establish a conventional tillage system. Therefore, the main function of primary tillage is to increase soil’s structural macroporosity. In spite of this, during secondary tillage operations on these freshly tilled soils, the traffic on seedbeds causes significant increases in soil compaction. The aim of this paper was to quantify soil compaction induced by tractor traffic on a recently tilled non consolidated soil, to match ballast and tyre size on the tractors used during secondary tillage. The work was performed in the South of the Rolling Pampa region, Argentina. Secondary tillage traffic was simulated by one pass of a conventional 2WD tractor, using four configurations of bias-ply rear tyres: 18.4×34, 23.1×30, 18.4×38 and 18.4×38 duals, two ballast conditions were used in each configuration. Soil bulk density and cone index in a 0 to 600 mm profile were measured before and after traffic. Topsoil compaction increased as did ground pressure. Subsoil compaction increased as total axle load increased and was independent from ground pressure. At heavy conditions, topsoil levels always showed higher cone index values. From 150 to 450 mm depth, the same tendency was found, but with smaller increases in the cone index parameter, 22 to 48%, averaging 35%. Finally, at the deepest layer considered, 600 mm, differential increases due to the axle load are great enough as to be considered similar to those found in the upper horizon, 36 to 64%, averaging 55%. On the other hand, bulk density tended to be less responsive than cone index to the traffic treatments. Topsoil compaction can be reduced by matching conventional bias-ply tyres with an optimized axle weight.     

基于多元线性回归分析的土坡有限元失稳判据定量研究

塑性区连通程度是有限单元法判别土坡是否达到极限状态的重要依据,鉴于此判据目前尚未取得统一,本文着重对均质土坡失稳判据进行了定量研究。在主要考虑对土坡稳定性影响较大的三大参数(黏聚力c、内摩擦角φ、坡比λ)的前提下,通过经典条分法选取了多组处于极限平衡状态的土坡参数组合,对这些参数组合进行有限元程序计算,求得极限平衡状态下土坡剪切带等效塑性应变中值连通率,再采用多元线性统计回归方法,得出塑性区中值连通率与土坡参数的关系公式y=0.020702c+0.024417φ-0.67898λ+0.46799,从而为土坡有限元稳定性分析提供了定量失稳判据,并且使得有限单元法与经典条分法计算成果具有一定的可比性。算例分析表明,利用本文判据公式得到的安全系数与Bishop法计算成果相吻合,从而验证了失稳判据公式的正确性。     

Study of the open and closed loop characteristics of a tractor and a single axle towed implement system

Accurate automatic guidance of towed implements is important for performing agricultural field operations and for gaining the ultimate benefit from such systems. The study of open and closed loop system responses of a vehicle-implement system can be helpful in the design of practical guidance controllers. Open loop analysis of the kinematic and dynamic models revealed that the higher order dynamics captured by the tractor and implement dynamic model had an impact on simulated responses at higher operating velocities and on higher input frequencies. In addition, a dynamic model with tire relaxation length dynamics was also studied. The various model responses were compared with the experimental responses. Closed loop system characteristics were studied by using a linear quadratic regulator (LQR) controller. The tractor position and heading and implement heading states along with respective rate states were fed back to close the loop. Steering dynamics were also added to the dynamic model closed loop analysis, which helped to achieve a realistic closed loop steering angle history. The closed loop system dynamics became faster as the forward velocity was increased. The open and closed loop response analysis performed in this work provided an understanding about the system at various forward velocities, which will help to design and develop efficient and robust tractor and towed implement guidance controller.     

A study on the effect of electronic engine speed regulator on agricultural tractor ride vibration behavior

In this study, the effect of electronic speed adjustment on tractor ride vibration levels is examined. With normal pedal operation the engine rotational speed drops with an increasing load. The electronic regulator provides a constant speed mode of operation independent of the load. Vibration levels were measured under different operating conditions and surfaces. As a first series of tests, the tractor was driven on a conglomerate bituminous track at speeds of 20, 25 and 28 km/h. Vibration was measured upon the surface of the operator seat simultaneously in the x, y and z directions. The reference axis system was that defined by the ISO 2631-1 [1]. The weighted r.m.s. acceleration was found to be between 8% and 8.6% higher for the case where operation with electronic speed adjustment had been selected. Secondly, cultivating was chosen as the field task and the vibration was measured while the tractor was traversing a rough farm track at speeds of 6, 7.5 and 9 km/h. In this case, the vibration levels with automatic speed adjustment were between 4.3% and 8.6% lower than when driving with normal foot pedal operation. From the above results, we may infer that electronic speed regulation should not be used in transportation on asphalt country roads. On the contrary, it seems that electronic regulation has an advantage when used in typical field tasks such as cultivating.     

Finite element analysis of tire traveling performance using anisotropic frictional interaction model

The traveling performance of off-the-road vehicles, such as construction machinery and exploration rovers, significantly depends on the interaction between the ground and the traveling mechanism, since inelastic ground deformation and frictional sliding phenomena are induced by the vehicle’s movement. In general, a tread surface causes anisotropic frictional interaction behavior on a macroscopic scale. In this study, an acceptable frictional interaction model was implemented to finite element method to rationally examine the anisotropic frictional interaction behavior between the tire and the ground. Finite element analysis of the single tire traveling performance, including certain slippage and side slip (skid), was then carried out to examine the effect of the anisotropic frictional interaction on the numerical results for the drawbar-pull and side force.     

The flow around a model helicopter main rotor in ground effect

Wind tunnel measurements of the wake below and ahead of a model helicopter main rotor in simulated forward flight in ground effect are presented. The wind tunnel used was equipped with a rolling road, and the ground speed was matched to the wind tunnel speed for a representative simulation in the wind tunnel of forward flight over the ground. Particle image velocimetry was used to investigate the structure of the wake, and it was observed that the moving ground had a remarkable effect on the flow; the wake is closer to the rotor and its size is reduced compared with the stationary ground case. The detailed distribution of vorticity within the wake is affected by the moving ground, and the mechanism for this is discussed in the paper.