VEHICLE PERFORMANCE IN DEEP SNOW UNDER LATE WINTER CONDITIONS - INFLUENCE OF PRESSURE DISTRIBUTION ALONG THE TRACK-SNOW CONTACT LENGTH

摘要

This paper is an experimental study of drawbar performance in deep snow under late winter conditions, and deals with the influence of the pressure distribution along the track-snow contact length on the tractive performance of a vehicle. The objective is to increase the knowledge about the influence of the design of the track assembly on the tractive performance of a skidsteered tracked vehicle in deep snow during the late winter. The tests were carried out by using a skid-steered tracked vehicle developed for the purpose by Bodin [I]. The design parameters studied are the influence of the longitudinal location of the centre of gravity, the nominal ground pressure and the influence of the distribution of the vehicle weight between the road wheels at rest on level hard ground. The most important result is that the drawbar pull increases when the centre of gravity moves forward. The increased drawbar pull originates mainly from an increased thrust between the tracks and the snow, which originates from a reduced trim angle of the vehicle. The reduced trim angle gives a more even normal pressure distribution along the track contact length, which increases the ability to transmit shear force between the tracks and the snow. Tests of the nominal ground pressure show that increased nominal ground pressure decreases the drawbar pull coefficient mainly due to a decreased thrust coefficient between the tracks and the snow. The reduced thrust coefficient is due to a considerable cohesive part of the shearing, especially for the internal shearing of the snow. By varying the amount of the vehicle weight carried by each road wheel, the influence of the pressure distribution along the track contact length on the tractive performance was tested. Three settings were tested: much of the weight carried in the middle, an even distribution and much of the weight carried by the corner road wheels. The results show that an even distribution or much of the weight carried by the corner wheels gives a higher drawbar pull than when much of the weight is carried by the road wheels in the middle which originates from a reduced trim angle of the vehicle.