Steering power ratio affected by soil sinkage with differential steering in tracked vehicle

Abstract: In order to study the steering performance of tracked vehicle adopting differential steering mechanism, the influence factors of steering power ratio need to be analyzed comprehensively. In early study, the influence factors of steering power ratio including turning radius, skid ratio and steering coefficient have been researched. Except those, steering power ratio of tracked vehicle is affected by the soil sinkage depth. At first, relationship between steering power ratio and sinkage was theoretically analyzed. Then the equation of steering power ratio, turning radius, skid ratio and sinkage was obtained. At the same time, steering power ratio is related to the soil parameters. In order to determine the soil parameters of the steering experiment ground, plate sinkage test was carried out. The test results showed that cohesive modulus of soil is 1.05933 kN/mn+1, frictional modulus of soil is 16.33049 kN/mn+2, deformation exponent is 0.6306. Then, experiments of considering the influences of sinkage and soil parameters were performed. A new measuring method has been proposed to reduce the experimental error of steering power ratio that the vehicle was steered in a small part of a circle instead of a full circle. The purpose is to reduce measuring error of steering power ratio caused by the different contact condition between track and ground. Experimental prototype was steered in large turning radius and in small on the ground in Northeast Agricultural University. Water content of soil is 12.09 %. The average value of soil shear modulus is 0.4529 m. Soil cohesion is 17716 Pa. Internal friction angle is 15.892 °. Through changing the rotational speed of the straight motor and steering motor, the different radius of experimental prototype can be implemented. The experimental data were recorded by sensors of moment and rotational speed, lap top and intelligent multi-channels recorder. Experiment value of steering power ratio can be calculated. Turning radius and central angle were measured by using T-ruler, tape, screwdriver and protractor. Use flour to mark the circle trace of the spot touching the ground which lies in the front and outside of the high speed track. Through drawing perpendicular bisector of two chords, center of circular trace could be got. Turning time was recorded by intelligent multi-channels recorder. According to the time from the beginning to the ending of steering motor's moment recorded by the recording device, the turning time could be obtained. Sinkage was measured by the self-made measurement device. After analyzing the experimental results, relationship among experimental turning radius, sinkage and experimental steering power ratio have been obtained. Steering power ratio was increased from 1.65 to 6.08. Sinkage was increased from 3.60 mm to 10.42 mm. Turning radius was reduced from 1.00 m to 0.29 m. Experiment results showed that steering power ratio increases as experimental turning radius decreases when tracked experimental prototype being steered on soft terrain. This is due to that track has lateral extrusion and push action to the soil. Contrary to that, the soil has an opposite action to track. When the rotational speed of the motor for steering was increased, turning radius was reduced. The greater the resistance of the track from soil was, the bigger steering power ratio was. Experimental sinkage increases as experimental steering power ratio increases. Because the bigger steering power ratio was, the greater lateral resistance between track and soil surface was, and sinkage was increased. At the same time, sinkage increases as turning radius decreases. The magnitude calculated based on the formula of steering power ratio is close to that measured by the test. The absolute error range is 0.16~1.74. The experimental results are in agreement with the theoretical analysis, and it can further perfect the tracked vehicle theory being steered differentially.