Tractive efficiency of four-wheel-drive vehicles: An analysis for non-uniform traction conditions

An analysis of the tractive efficiency of four-wheel-drive vehicles is conducted from the perspective of maximizing efficiency of slip with respect to non-uniform traction conditions in particular. The analysis is conducted using a more rigorous mathematical analysis than previously and using a thorough graphical analysis to substantiate the mathematical analysis. Previous studies concluded that under all traction conditions efficiency of slip will be a maximum when the slip of each wheel is equal. The analysis revealed that, contrary to the previous literature, efficiency of slip will not be a maximum when the slip of each wheel is equal under non-uniform traction conditions. When applied to a vehicle with an interaxle fixed ratio coupling, this means that the optimum theoretical speed ratio is not always equal to 1. An example of non-uniform traction conditions is the situation where two drive wheels are on soil and the other two are on tarmac. The improvement in the efficiency of slip, in this example, when using the correct theoretical speed ratio (as opposed to that equal to 1) is particularly marked at high drawbar loads. The method by which the correct theoretical speed ratio is to be achieved when non-uniform traction conditions occur is problematic. The drive system would require a drive mechanism and a level of intelligence not currently found in off-road vehicles.

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Optimization of the tractive performance of four-wheel-drive tractors: Theoretical analysis and experimental substantiation

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1243/0954407981525966 ◽

1998 ◽

Vol 212 (4) ◽

pp. 285-297 ◽

Cited By ~ 13

Author(s):

J. Y. Wong ◽

N. B. McLaughlin ◽

Z Knezevic ◽

S Burtt

Keyword(s):

Theoretical Analysis ◽

Field Test ◽

Angular Speed ◽

Speed Ratio ◽

Torque Distribution ◽

Wheel Drive ◽

Four Wheel Drive ◽

Tractive Efficiency ◽

Driving Torque ◽

Experimental Substantiation

The results of a theoretical analysis reveal that, for a four-wheel-drive tractor to achieve the optimum tractive performance under a given operating condition, the thrust (or driving torque) distribution between the front and rear axles should be such that the slips of the front and rear tyres are equal. For four-wheel-drive tractors with rigidly coupled front and rear drive axles, this can be achieved if the theoretical speed (the product of the angular speed and the free-rolling radius of the tyre) of the front and that of the rear wheels are equal or the theoretical speed ratio is equal to 1. Field test data confirm the theoretical findings that, when the theoretical speed ratio is equal to 1, the efficiency of slip and tractive efficiency reach their respective peaks, the fuel consumption per unit drawbar power reaches a minimum, and the overall tractive performance is at an optimum.

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The Issue of Forced Labour in the Onjembo: German South West Africa 1904–1908

Itinerario ◽

10.1017/s0165115300021203 ◽

1995 ◽

Vol 19 (1) ◽

pp. 97-104

Author(s):

Jan-Bart Gewald

Keyword(s):

Sand Dunes ◽

Prisoners Of War ◽

Road Vehicles ◽

Mass Graves ◽

True Nature ◽

South West ◽

Wheel Drive ◽

South West Africa ◽

Forced Labour ◽

Four Wheel Drive

Visitors to the sea-side resort of Swakopmund on the Namibian coast will have often stood on the northern banks of the Swakop river and marvelled at the sea of sand dunes that commences on the opposite side of the river. Very few of them will ever have realised that they were standing upon, and wandering amongst, the mass graves of Herero and Nama prisoners of war, who between 1904 and 1908 were employed as forced labourers. As I write the mass-graves of Swakopmund are used by recreationers as a testing ground for their four-wheel-drive off-road vehicles, perhaps in the future the true nature of these graves will come to be realised and appreciated.

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