Maximum Tractive Efficiency Research Articles

Tractive efficiency of a tracked vehicle

This paper deals with the problem of evaluating the tractive efficiency of tracked vehicles. The tractive efficiency concept used is identical to that introduced by Wismer and Luth for wheeled vehicles. In this paper, the tractive efficiency relevant to the track is derived analytically. The resulting expression is a function of the soil strength parameters, vehicle weight, track dimensions, track slip and the transmission coefficient. It is noteworthy that despite the difference in vehicle systems (tracked versus wheeled), and in investigation methods (analytical versus semi-empirical), the expression derived in this paper and that suggested by Wismer and Luth are quite similar. The analysis performed shows that the tractive efficiency function necessarily has a maximum defined by an optimum slip value. It is analytically proven that the maximum tractive efficiency and the maximum tractive force cannot be achieved simultaneously. Nevertheless, the numerical results show that a satisfactory compromise can be achieved. The results of a comparative analysis support the common experience that the tractive efficiency of a track is usually higher than that of a wheel.

Ballast and Inflation Effects on Tire Efficiency

ABSTRACT THIS report deals with the interactive effects of ballast and inflation pressure on tractive efficiency of selected bias- and radial-ply tractor tires operated under field conditions. Results indicated that if control systems were available to select ballast and inflation pressure levels for maximum tractive efficiency, the gains in tractive efficiency would be up to 0.21.

Ballasting wheeled tractors to achieve maximum power output in frictional-cohesive soils

Empirical equations developed previously are used to construct a curve giving the drive tyre load per unit of available axle power which is required to ensure that a drive tyre can work at maximum tractive efficiency at any forward speed. A curve showing the required wheelslip for maximum efficiency is given. The same equations are used to derive curves which show the loss in tractive efficiency resulting from the tyre load being greater or smaller than the optimum value. It is shown that when a dimensionless parameter, which is named the ballast number, drops below a certain value then a tyre cannot transmit all the power available. Maximum output in these circumstances is governed by a parameter called the output coefficient. Maximum values of the output coefficient are given as well as the wheelslip at which these occur. Curves showing the values of ballast number required to ensure that the tyre can transmit all the available power at any value of slip are given. The results of field experiments on ballasting of wheeled tractors are given and these are explained by use of the theoretical curves. The requirements for optimizing work rate are examined. It is emphasized that thes results apply to frictional-cohesive soils only and should not be extrapolated to purely frictional or purely cohesive soils.

A preliminary investigation of a combined slip and draught control for tractors

During the field operation of tractors, a significant portion of the energy is lost in slippage of the traction wheels. In the existing control systems based on the load on the tractor, for example draught and drive-line torque control, the operator has to set the control system manually depending on varying soil conditions. In this research, the slip of the traction wheels was used to set the control system in order to improve the utilization of engine power. The factors affecting the tractive efficiency and the conditions at which maximum tractive efficiency can be achieved are discussed. Of the 2 requirements suggested, namely adjusting the axle load and adjusting the coefficient of traction or wheel slip, as a first step, only slip control was used in this research. The slip of the rear traction wheels with respect to the front wheels was found using photo-transistors and electronic circuits. An analogue output of the slip activated a 12 V/d.c. motor whenever the slip deviated from the desired (set) level. The motor through a gear train rotated the draught control shaft of the tractor hydraulics. The implement is lifted whenever the slip increases beyond the desired level, and lowered when the slip decreases. Field trials showed the possibility of maintaining any desired level of slippage. Experiments on tractor hydraulic response with the slip control system showed that the response of the new system was slowed down by the high torque requirement to move the draft control shaft. The combination of the slip control system with the present draught control system was found to give good field performance.

Tractive efficiency of soil under a simple traction device

The efficiency with which a soil can transmit energy from a traction device on a tractor to the drawbar has been called the tractive efficiency of soil. It varies with normal pressure and soil deformation. Tractive efficiency of soil was calculated considering the shear force (thrust force) produced for a given normal pressure and shear and vertical displacement and corresponding energy losses under a simple traction device. Relationships between average shear force per unit area, normal pressure and shear deformation were obtained at maximum tractive efficiency. Calculated tractive efficiencies of soil were compared with measured tractive efficiencies of a test wheel under similar conditions. There was good agreement for low sinkage of the test wheel.

Tractive Efficiency—Maximum or Optimum?

ABSTRACT MAXIMUM tractive efficiency usually occurs at a gross traction ratio of 0.4 to 0.5. On concrete this point is attainable at high forward speeds not suitable for most field operations. Various combinations of forward speed and drive wheel load can be used. A compromise exists in field operations between speed and ballast for maximum tractive efficiency, highest field capacity or productivity and minimum capital costs. A load to power ratio of approximately 60 kg/kW for two wheel drive tractors operating at wheel speeds in the range of 8 to 12 km/h results in optimum tractive efficiency and optimum performance.

Tractive performance of tractor drive tyres: III. Running in the furrow bottom

The tractive performance of a 13·6–38 and a 16·9–34 tractor drive wheel tyre was measured when running in a 356 mm (14 in) furrow and on the surface of the same field, in 24 different field conditions over a 2-year period. When tractiion conditions were normal (soil cone index valueless than 1000 kPa) both tyres gave an average 25% increase in maximum coefficient of traction and 14% increase in coefficient of traction at 20% slip when running in the furrow. Maximum tractive efficiency in the furrow was the same as that on the surface. When traction conditions were good (soil cone index value greater than 1000 kPa) both tyres gave an average 23% increase in maximum coefficient of traction when running in the furrow but the coefficient of traction at 20% slip was the same in the furrow as on the surface. Maximum tractive efficiency in the furrow decreased by an average of 10% for the 13·6–38 tyre and 15% for the 16·9–34 tyre.

Comparison of the tractive performance of a tractor driving wheel during its first and second passes in the same track

Abstract The tractive performance of a conventional 13.6–38 tractor driving wheel tyre was measured in 19 different fields using the NIAE Single Wheel Tester. In each field the performance was measured on the undisturbed ground and again in the rut formed by a previous run with the same tyre. The second run simulated the operation of the rear wheels on a four-wheel drive tractor. The performance during the second pass was generally better than during the first pass. On average, the coefficient of traction increased by 7%, rolling resistance reduced by 11% and maximum tractive efficiency increased by 5%. The improvement increased as ground conditions deteriorated but was never large enough to fully explain the differences in performance between two and four-wheel drive tractors previously measured. It is suggested, therefore, that these differences may be primarily due to the greater ease with which power, weight, implement size and working speed can be matched with four-wheel drive tractors.

Using Dimensionless Prediction Terms to Describe In-Soil Tracked Vehicle Performance

ABSTRACT j ABORATORY tests were con-1^ ducted with a single model track operating straight line at low speed in level test beds of air-dry sand and of near-saturated clay. Dimensionless terms composed of independent (con-trolled) track and soil variables were developed to predict track perform-ance in the two soil types. Four performance levels (the towed, self-propelled, 20 percent slip, and maximum tractive efficiency condi-tions) and five performance variables (pull, towed force, torque, sinkage, and trim angle) are considered. Validation tests indicate that both the sand and the (preliminary) clay prediction terms can be used to describe prototype vehicle perform-ance

The field performance of some tractor tyres related to soil mechanical properties

The tractive performance of five sizes of tractor driving wheel tyres were measured in thirteen field conditions during the autumn and winter of 1971–1972 using the N.I.A.E. Single Wheel Tester Mk II. The results indicated that reducing inflation pressure produced a significant increase in coefficient of traction and increasing section width produced a significant reduction in rolling resistance. Investigation of methods of predicting tractive performance from soil measurements suggested that soil shear strength and soil-rubber friction were likely to provide a better indication of coefficient of traction than would cone penetrometer measurements but that the cone penetrometer would provide useful indications of coefficient of rolling resistance and maximum tractive efficiency.