1,720,961 research outputs found
Soluzioni per ridurre le perdite di potenza in una trasmissione di trattrice agricola
No full textLa riduzione delle perdite di potenza è oggi uno dei principali obiettivi nello sviluppo delle trasmissioni delle trattrici agricole. Recenti studi effettuati sugli assorbimenti di potenza all’interno di una trasmissione full power-shift hanno permesso di individuare le condizioni nelle quali si hanno maggiori perdite e gli elementi che influenzano tali assorbimenti. In particolare le marce nelle quali si hanno maggiori perdite sono quelle dove si hanno velocità di avanzamento maggiori. In tali marce le perdite sono causate per circa il 50% da resistenze passive, attriti e frizioni della trasmissione, mentre il 40% è causato dall’olio presente all’interno della trasmissione. Queste ultime sono in parte provocate da livelli di olio non regolari all’interno delle scatole dei freni. In tale contesto l’obiettivo del lavoro è quello di proporre e verificare sperimentalmente soluzioni che permettano di ridurre le perdite di potenza all’interno di una trasmissione full power-shift. Le prove sono state effettuate su una trasmissione della New Holland installata su un trattore da 140 kW. Gli assorbimenti di potenza sono stati valutati misurando la potenza necessaria per trascinare la trasmissione con un motore elettrico. Le principali soluzioni adottate riguardano la conformazione della scatola della coppia conica ed il processo di lavorazione dei dischi delle frizioni. Tali soluzioni hanno permesso di ridurre le perdite di potenza all’interno della trasmissione di circa il 15%. Le modifiche introdotte nelle scatola della coppia conica hanno inoltre consentito di equilibrare le portate di olio all’interno delle scatole dei freni e di ridurre le temperature di esercizio
Experimental evaluation of power losses in a power-shift agricultural tractor transmission
No full textThe results of tests on a full power-shift transmission, suitable for use on a 140 kW, agricultural tractor are reported. The aims of the research were to evaluate the working conditions where there are higher power losses, and to identify the causes of energy dissipation. The tests were carried out with the transmission set in motion and the power absorbed in each gear was evaluated. Following identification of the gears in which the higher losses were measured, the components were separated, one at a time, from the transmission and the influence on the losses measured. The results showed that higher losses occur in higher gears. The tests indicated that 52% of the total losses are caused by passive resistance and friction in the transmission together with the power absorbed by the hydraulic circuit in the neutral position, 40% by oil splashes in the transmission, 4% by the brakes, and 4% by the final reducers and corresponding sun wheels
Methodology for the realisation of accelerated structural tests on tractors
No full textThe most significant efforts to reduce the development costs on tractors have been concentrated by manufacturers on the attempt to decrease the costs of experimental testing. The validation of tractor prototypes is presently performed with a replication of
a particularly harsh condition a defined number of times. Field tests are also carried out to evaluate the prototype during real use, but it is difficult to perform such tests for a long enough period to achieve reliable results. In this context, accelerated tests have been
introduced in the automotive sector and on tractor components. The goal of this paper is to define a methodology to perform accelerated structural tests on tractors, through the reproduction of real customer tractor usage. A market analysis was performed on a 80 kW power tractor and a series of measures were then taken to simulate the real use of the tractor. Subsequently, rainflow matrixes of the signals were extrapolated and used to estimate the tractor loads for 10 years of tractor life. Finally these loads were reproduced on testing grounds with special road pavements. The results obtained highlight the possibility of reproducing field loads during road driving on proving grounds, but the use of field
operations is also necessary. The global acceleration factor obtained in this first step of the methodology is equal to three but can be increased
Flow-forces effect on the behavior of an open center hydraulic distributor
No full textThe effect of steady-state axial flow-forces on the motion of an open center hydraulic distributor notched spool is considered. More in details, the spring driven spool centering is considered, in which undesired axial flow-forces could overcome the spring action. A steady-state analysis of the forces influencing the spool motion is reported, calculating the axial flow-force for different positions of the spool. Different notched shapes of the metering edge are considered, and an optimized solution for the notched edge of the spool is proposed at last
Evaluation of oil flows for the lubrication of an agricultural tractor transmission
No full textAn important part of power losses in tractor transmissions is due to the oil they contain. To limit power losses, a reduction in oil level in the tractor drive train is necessary, while still ensuring lubrication of the individual components. In this article, oil flows sufficient for the lubrication of gears and bearings in a full power-shift transmission front box were calculated. After evaluation of individual element power loss in the worst working condition, a thermal balance and the oil flow required to eliminate the produced heat were calculated. Gear lubrication requires about 10 L min-1, while rolling bearings need about 2 L min-1. Two gear jet flow lubrication systems were then evaluated and the most important parameters established for correct nozzle positioning
Design of the lubrication circuit of an agricultural tractor
No full textToday the design of hydraulic and lubrication circuits is becoming more and more important. The aim of this study is to develop a methodology for the design of the lubrication circuit of an agricultural tractor. In this paper the lubrication circuit of a continuously variable transmission is analysed. Several lines of the circuit are considered and in particular the lubrication of gears is discussed. The worst possible working condition which corresponds to the highest power dissipation for each part of the transmission is determined. The model of the lubrication circuit is developed with two different software simulations. In order to check the reliability of the simulation models and to characterise the lubrication circuit, experimental tests are performed. The comparison between the values of pressure drops obtained by the models and by the experimental test, demonstrates that it is possible to use these programs for the set up of a simple model of the lubrication circuit. The calculation of oil flows necessary for a force-fed lubrication of the gears, the simulation of the circuit by a commercial software, and the validation of the circuit design allow to set up a preliminary equilibrium among the pipes and a proper flow rate distribution. Optimising the circuit design in the initial phase of the project is very important. The experimental adjustment of the circuit, which is often difficult, can be simplified; time and cost production can be reduced
Design optimization of Input and Output Coupled power split Infinitely Variable Transmissions
No full textThe authors present an optimization procedure in designing infinitely variable transmission architectures, which allows them to achieve a significant reduction in power recirculation and, hence, an increase in mechanical efficiency. The focus of this paper is on infinitely variable transmissions used in off-highway vehicles and, in particular, on input and output coupled architectures. The optimized solutions have been analyzed in depth, with particular attention to the power flowing through the infinitely variable unit, which strongly influences the overall efficiency of the transmission. The major result of this study is that the so far neglected output coupled solution, if properly optimized, guarantees very good performance over the entire range of vehicle speed. The analysis then shows that the particular choice of either input or output coupled architecture by itself, or of a mixed solution, strictly depends on the specific application under consideration and that none of them should be discarded a prior
Tractor accelerated structural testing by means of the rainflow method.
No full textThe 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
Dynamic modeling and control of electro-hydraulic wet clutches
No full textThis paper proposes an energy-based detailed dynamic model of an hydraulic multi-plate clutch actuator controlled by an electro valve with internal pressure feedback. The proposed system model has been validated by comparison with experimental measurements. Based on the main features of the electro-hydraulic clutch actuator system, two clutch pressure control strategies are proposed and the tracking performances are tested through simulation experiments
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