Tractor accelerated test on test rig

The experimental tests performed to validate a tractor prototype before its production, need a substantial financial and time commitment. The tests could be reduced using accelerated tests able to reproduce on the structural part of the tractor, the same damage produced on the tractor during real life in a reduced time. These tests were usually performed reproducing a particular harsh condition a defined number of times, as for example using a bumpy road on track to carry out the test in any weather condition. Using these procedures the loads applied on the tractor structure are different with respect to those obtained during the real use, with the risk to apply loads hard to find in reality. Recently it has been demonstrated how, using the methodologies designed for cars, it is possible to also expedite the structural tests for tractors. In particular, automotive proving grounds were recently successfully used with tractors to perform accelerated structural tests able to reproduce the real use of the machine with an acceleration factor higher than that obtained with the traditional methods. However, the acceleration factor obtained with a tractor on proving grounds is in any case reduced due to the reduced speed of the tractors with respect to cars. In this context, the goal of the paper is to show the development of a methodology to perform an accelerated structural test on a medium power tractor using a 4 post test rig. In particular, several proving ground testing conditions have been performed to measure the loads on the tractor. The loads obtained were then edited to remove the not damaging portion of signals, and finally the loads obtained were reproduced in a 4 post test rig. The methodology proposed could be a valid alternative to the use of a proving ground to reproduce accelerated structural tests on tractors

Tractor accelerated test on test rig.

The experimental tests performed to validate a tractor prototype before its production, need a substantial financial and time commitment. The tests could be reduced using accelerated tests able to reproduce on the structural part of the tractor, the same damage produced on the tractor during real life in a reduced time. These tests were usually performed reproducing a particular harsh condition a defined number of times, as for example using a bumpy road on track to carry out the test in any weather condition. Using these procedures the loads applied on the tractor structure are different with respect to those obtained during the real use, with the risk to apply loads hard to find in reality. Recently it has been demonstrated how, using the methodologies designed for cars, it is possible to also expedite the structural tests for tractors. In particular, automotive proving grounds were recently successfully used with tractors to perform accelerated structural tests able to reproduce the real use of the machine with an acceleration factor higher than that obtained with the traditional methods. However, the acceleration factor obtained with a tractor on proving grounds is in any case reduced due to the reduced speed of the tractors with respect to cars. In this context, the goal of the paper is to show the development of a methodology to perform an accelerated structural test on a medium power tractor using a 4 post test rig. In particular, several proving ground testing conditions have been performed to measure the loads on the tractor. The loads obtained were then edited to remove the not damaging portion of signals, and finally the loads obtained were reproduced in a 4 post test rig. The methodology proposed could be a valid alternative to the use of a proving ground to reproduce accelerated structural tests on tractors

Prediction of whole body vibration through a multibody model of a tractor seat

The vibrations transmitted to the driver induce permanent and temporary damage to the body. The agricultural tractors are characterized by a vibration level that can be higher than the exposition level fixed by the 2002/44/EC, in some conditions. The vibrations on tractors have a high intensity and a low frequency with the consequence of difficulties in the project of suspension systems able to reduce the intensity of the level. The numerous innovative suspension systems studied in the recent years, as the active and semi-active seats, did not introduce significant improvements. In the present paper a multibody model of a seat suspension system to an agricultural tractor with a 170 kW power, has been defined with the goal to predict the seat acceleration and evaluate the reduction of the vibration level transmitted to the driver

Optimal three-point hitch design to maximize lifting performance

The three-point hitch mounted on tractors was introduced by Ferguson in 1935 and has been modified from the first patent with the introduction of different controls. In recent years, the geometry has not been significantly modified due to the standards that define the application limits. These standards define the geometric constraints of the system as a function of the tractor power and wheelbase. The constraints have been fixed to standardize the connection with implements and limit their movements. The degrees of freedom could be used to optimize the three-point hitch as a function of the design specifications, and in particular to optimize the maximum lifting capacity. Analysis of OECD-Approved reports, confirmed by the authors' experience, shows a high number of three-point hitches with a maximum lifting capacity that is not optimized. The goal of the present work is to provide a design tool to optimize the three-point hitch by maximizing the lifting capacity and satisfying the constraints fixed by the standards. The methodology proposed uses a constrained optimization technique and was validated on an existing three-point hitch. The optimized three-point hitch permits a maximum lifting force about 25% greater than the existing value. The lift arm length, the lower link length, and their pivot point positions are the variables with greatest influence on the objective function. The constraint of a minimum angle of 10\ub0 between the mast and the vertical axis is the most limiting constraint on the objective function

Towards more efficient tractors: Assessing and refining traction test procedures for agricultural tractors

A reliable testing procedure is needed to benchmark different vehicle and tyre parameters. Several testing procedures within two main families – transient and steady states – were adopted to evaluate drawbar performance of tractors. The two procedural families were not hitherto compared using a full vehicle. This article aims to fill this gap. The transient and steady-state procedures were tested using a tractor rated of 230 kW sets in different configurations and equipped with sensors for evaluating the tractive parameters. In the transient procedure, the drawbar load was continuously increased to maintain a fixed ground speed. In the steady-state procedure, the drawbar load was gradually increased by reducing the ground speed. The maximum drawbar force generated by the tractor differed little between procedures, but a difference was observed in power delivery efficiency, mostly for the transmission’s influence during transient conditions leading to variable transmission efficiency. The results of the steady-state procedure for different vehicle configurations were more consistent with findings in the literature than those of the transient procedure. The steady-state procedure is better than the other but it requires more land and therefore it is less convenient when drawbar performances must be quickly evaluated for many vehicle and soil configurations

Optimization of a three point hitch in an agricultural tractor

The three point hitch was fitted on a tractor for the first time by Ferguson in 1935, and has been modified in the following years till the electronically controlled modern versions. During the last decades the geometry of the three point hitch has been regulated from standards. In particular, the ISO 730 specifies the geometrical constraint of the system in function of the tractor power and the physical and dimensional parameters as the mass and the wheelbase of the tractor. These constraints have been fixed to restrict the implement movements and, as a consequence, to reduce the risks related to the use. The directive 74/151/CEE determines limits on the maximum load on the front axle of the tractor and, as a consequence, on the maximum lifting load by the three point hitch. This constraint has been imposed to guarantee tractor stability. The remaining degrees of freedom are usually used from the designers to maximize the lifting load. This measure is also required by the OECD Code 2 standard. The goal of the paper is to define a methodology in order to design the three point hitch of a tractor, able to respect the standard ISO 730, the tractor stability according to the directive 74/151/CEE, and maximize the lifting load using a constrained optimization technique. An optimization problem with constraints has been defined using as its objective a function to maximize the equation that defines the lifting load capacity in function of the three point hitch geometry, and fixing the force deriving by the hydraulic cylinders. The constraining equations have been defined according to the standard ISO 730 with respect to the geometric limits of the three point hitch and according to directive 74/151/CEE with respect to the dynamics of the tractor. The vertical and horizontal distance of the lower link pivot point, of the upper link pivot point and of the lift arm pivot point from the real-wheel axle; the length of the upper link, of the lift arms, of the lower links, and of the lift rods; the stroke of the cylinder and the distance of lower link pivot points to lift rod pivot have been defined as variables. The methodology has been used to design a three point hitch for a specific tractor and to perform a sensitivity analysis to analyze the influence of each variable on the load capacity of the three point hitch, showing the crucial designing variables. The optimization technique firstly permitted to design the three point hitch in a reduced time, and also allowed to give some guidelines on the dimensioning through the sensitivity analysis. The sensitivity analysis has shown how the length of lift rods allows to increase the load capacity of the hitch as well as the regulation range. The distance of lower link pivot points to lift rod pivots is the parameter that deeply influences the uniformity of the load capacity in the height range

Structural Strength Evaluation of Driver\u2019s Protective Structures for Self-Propelled Agricultural Machines

The high number of accidents due to rollovers of agricultural machines has increased the interest of researchers and organizations for standardization in this field. In the 1960s, standards to test rollover protective structures (ROPS) for tractors were designed and approved. Similar standards were introduced in the 1990s for earth-moving machinery, but ROPS standards were not defined for self-propelled agricultural machines. In the present work, the driver's protective structures of five different categories of self-propelled agricultural machines were analyzed with the goal of introducing ROPS with a strength level in accordance with the standards used for tractors while maintaining the same shape as the existing structure. The results show a low resistance level of the present structures on the machines selected for the tests. New structures that are able to sustain the loads specified by the tractor standard are not different in design from the existing structures, but an increase of the resistance of the materials or an increase of the thickness of the mountings is necessary

Tractor accelerated structural testing by means of the rainflow method.

The remarkable developments in agriculture in recent years and the needs of customers to improve machinery in order to meet the demands of such technological developments, have driven tractor manufacturers to reduce product life and, as a consequence, development costs. The sector in which the most significant efforts have concentrated on in the attempt to decrease such costs, is that of experimental testing, so as to validate the prototype of tractors. Presently, in fact, many tractor companies rely on tests based on experience that replicate a particularly unfavourable condition a defined number of times. These tests, even if long and costly, do not always faithfully reproduce the real use of the tractor. Therefore, field tests are also carried out to evaluate the prototype during real use, but it is difficult to perform such tests for a period of time long enough to be efficient. In this context, accelerated tests have been introduced, producing a certain damage to the structure in a reduced amount of time, replicating customer use. The goal of this paper is to define a methodology for the realization of accelerated tests on a tractor, through the reproduction of real customer tractor usage. A market analysis was performed to estimate the customer usage of a 80 kW power tractor. The tractor was instrumented with strain gauges able to record the most significant loadings on the main components. A series of measures were then taken to simulate the real use of the tractor. Subsequently, the rainflow matrixes of the signals were extrapolated and used to estimate the tractor loadings for 10 years of tractor life. Finally, there was an attempt to reproduce these loadings on proving grounds with special road pavements. The results obtained highlight the possibility of reproducing field loadings during road driving and that of carrying out tractor testing in a reduced timeframe