Improvement of automatic control of tractive modes of earthmoving and haulage machines during technological operations

Abstract

The tractive mode of a tracked earthmoving and haulage machine is shaped at the intersection of three constraints: the adhesion capacity of the undercarriage, the available power of the engine and the variable resistance of the working equipment, which grows as the blade load accumulates. Regulatory documents fix limiting slip values for drawbar testing, whereas in-service automatic control systems are built upon criteria that are not aligned with these values, so that the computed optimum of the duty cycle and the regulatory boundary diverge. The purpose of the work is to quantify the effect of the transition from single-loop control of blade depth by slip to two-loop control that combines blade depth regulation with continuous variation of the hydrostatic transmission ratio according to engine load. The calculation was carried out on the author's model of a tracked bulldozer of tractive class 15 with an operating mass of 27,4 t; the interaction of the undercarriage with the soil was described by an exponential dependence of the adhesion coefficient on slip, and the duty cycle was reproduced by numerical integration with a step of 0,02 s for three soil conditions and three haulage distances. Two-loop control raises technical productivity by 18,9% on light loam, by 10.0% on soft plastic clay and by 6.6% on heavy loam, while specific fuel consumption decreases by 8,1, 3,7 and 0,3% respectively, and the utilisation factor of rated engine power rises from 0.807-0.874 to 0.954-0.956. Decomposition of the gain by the method of chain substitutions attributed 45,0% of the effect to the reduction of haulage time, 31,5% to the reduction of cutting time and 23,5% to the return run. Sensitivity of the result to the lag of the blade depth loop on homogeneous soil within the range 0,10-0,80 s did not exceed 1,2 percentage points, yet when soil conditions change within a single pass the time required to leave the zone of limiting slip differs sixfold. The governing parameter of the tractive mode is the slip setpoint rather than the speed of the actuator: the computed optimum of the cycle lies above the permissible regulatory boundary, and attainable productivity is limited by the requirements of undercarriage and subgrade preservation.