The article is described the design of the mechanism for changing the clearance of the rear axle of a universal-tiller tractor from a low-clearance to a high-clearance position and vice versa. The most loaded place in the design of the mechanism for changing the clearance of the rear axle, which is the clip, is determined. The dynamic analysis of the load on the cage for three cases of loading in two sections passing through the bearing supports is carried out. At the same time, the main recommendations are aimed at ensuring a sufficient margin of safety in dangerous sections of the cage. In particular, one of the ways to ensure a sufficient margin of safety in dangerous sections of the cage is to use a material for its production - 45L steel. In Central Asia, all mechanized work on inter-row processing of cotton crops is carried out by a three-wheeled tractor adapted to the natural and production conditions of the region. Studies have established a negative technogenic impact of the front wheel of a three-wheeled tractor on the soil, which is eliminated by the use of a four-wheeled tractor. However, its use is constrained by the inadequacy of the agrotechnical passage. To solve this problem, LLC “DTCAM” is developing a four-wheeled tractor equipped with mechanisms for changing clearance, which provides sufficient agricultural cultivation for inter-row processing of cotton crops. Identification of dangerous places in the design of the mechanism for changing the clearance of the rear axle and dynamic analysis of the loads at this place, preventing breakdowns, increases the reliability of this tractor. It has been revealed that one of such dangerous places is a cage connected to the DCT cover, which accepts the main load transmitted from the tractor to the wheels and back. Dynamic analysis of the cage loads for various cases of loading in two sections passing through the bearing supports showed that the most loaded section is the section of the bearing support located on the DCT side. There is an insufficient margin of safety in this section when the tractor moves along irregularities. To ensure reliable operation, it is recommended to introduce the hardening of the cage area from the DCT side, where the bearing of the mechanism for changing the clearance of the rear axle is at least 35 HRCe, or use material - steel 45L.

The authors noted the disadvantages of the 3-wheel universal row-crop tractor. To eliminate them, LLC Design and Technological Center for Agricultural Engineering developed a 4-wheel universal row-crop tractor with variable ground clearance.(Research purpose) To determine the pressure change in the hydraulic system and the transfer time of the rear axle from one type of clearance to another.(Materials and methods) The authors showed that the rear axle clearance could be changed using a special mechanism - with minimal labor costs, without the use of lifting equipment and assembly and dismantling works. They explained that the mechanism was driven by a working hydraulic cylinder. The experiments were carried out on a prototype tractor with adjustable ground clearance, equipped with a separate-aggregate hinged system at an engine speed of 1200-2000 rpm (revolutions per minute). M10G2K oil was used in the hydraulic system, heating it to 65 degrees Celsius (at an ambient temperature of 33-35 degrees Celsius).(Results and discussion) The hydraulic system consisted of an NSh-32 hydraulic pump, a P80 hydraulic valve, two Ts50-200 working hydraulic cylinders, a double-acting hydraulic lock, a hydraulic tank, filters, hoses and high pressure pipes. At the inlet and outlet channels of the working hydraulic cylinders, which activated the mechanism for changing the rear axle clearance, hydraulic locks were installed, and diaphragm pressure sensors model SS302 from Sendor Sensor with a measurement range from 0 to 40 megapascals were placed along the hydraulic line connecting the hydraulic locks with the hydraulic valve.(Conclusions) The authors determined that the time for transferring the rear axle from low clearance to high was 2.2-4.4 seconds, and the pressure in the hydraulic system was 3.8-16.4 megapascals at an engine speed of 1300-2000 rpm. It was found that when transferring from high to low ground clearance, these indicators amounted to 1.0-1.4 seconds and 0.99-9.90 megapascals.

In accordance with the agricultural row-crops cultivation practices adopted in the Central Asian region, machine-tractor units carry out a large number of passes through the field during the growing season. Consequently, individual sections of the fields are repeatedly affected by the running systems of these machines, which negatively affects soil fertility. The universal row-crop tractors used in cotton production have two types of wheel arrangements: 3W2 and 4W2. Consequently, these arrangements have different natures and magnitude of impact on the soil. Despite a number of advantages of 4-wheeled tractors due to insufficient agrotechnical clearance under the front and rear axles beam, they are not used for inter-row cotton cultivation. Mechanisms including a stepless change in ground clearance, both for the front and rear axles of a 4-wheeled tractor, eliminate these disadvantages and thereby expand the possibilities of their use. The use of a 4-wheeled tractor in field and transport operations has shown that the most loaded parts in the developed mechanism for changing the clearance of the rear axle are rolling supports of the cage on the casing of the rear axle of the tractor.

An increase in the power of the high-clearance tractor with the 3K2 wheel configuration (TTZ-811) and the weight of the machines coupled with it has led to an increase in the pressure of its running elements on the soil. The authors have proposed to replace it with a tractor with the 4K2 wheel configuration with an adjustable ground clearance (TTZ-1033), which has several advantages.Research purposeThe study of the effect of the wheel configuration, travel speed and air pressure in the tire on the tractor's front wheel pressure on the soil.Materials and methodsThe authors have analytically determined the relationship between the contact area of a wheel tire with the soil on the tire parameters and the internal air pressure in it. To take measurements, load TAS607 sensors like with specially made nozzles have been used.Results and discussionIt has been found that under similar conditions, the average pressure on the soil in the layer of 10-50 centimeters across the width of the front wheel tire of TTZ-811 is 19.0-27.6 kilopascals more as compared to TTZ-1033. It has been found that an increase in air pressure in the tire from 1.2 to 2.2 megapascals results in a n increase in average front wheel pressure on the soil in the seed layer (0-10 centimeters) of the TTZ-1033 tractor from 61.9 to 70.8 kilopascals, and of the TTZ-811 tractor – from 63.5 to 79.3 kilopascals. It has been revealed that at a depth of 10 centimeters, the pressure of the front wheel of the TTZ‑1033 tractor averaged 84.9-108.2 kilopascals, and at a depth of 50 centimeters – only 12.2-12.8 kilopascals. Under the same conditions, the average pressure` of the TTZ-811 tractor's front wheel decreases from 78.0-113.3 to 15.3-52.8 kilopascals.ConclusionsThe authors have stated that soil compaction with the front wheels of a tractor can be reduced by replacing a tractor with a 3K2 wheel configuration with a tractor with a 4K2 wheel configuration, as well as by increasing the tractor speed.

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