SELECTION FRONT AXLE DESIGN FOR HIGH CLEARANCE AND HIGHLY MANEUVERABLE COTTON TRACTOR

ABSTRACT

The article presents some results of research conducted at the "Design and Technological Center of Agricultural Engineering LLC"  ("DTCAE" LLC) to create a high-clearance and highly maneuverable front axle for cotton-growing four-wheeled universal row-cultivator tractors. The design features of the developed front axle device are given. The technical solution adopted in the design of the mechanism for turning the guide wheels of this front axle is described. The device and principle of operation of the mechanism for turning the guide wheels and various modes of its operation are given. The steering wheel turning mechanism used on the front axle allows for two transport control functions: turning the steering wheels according to the traditional scheme for movement in the transport-working mode and turning the steering wheels in opposite directions for turning on the spot. The innovation applied on the front axle improves the steerability of the steering wheels and ensures minimization of the turning radius of the tractor.

АННОТАЦИЯ

В статье приводятся некоторые результаты исследований, проводимых в ООО «Конструкторско-технологический центр сельскохозяйственного машиностроения» (ООО «КТЦСМ») по созданию высококлиренсного высокоманевренного переднего моста к хлопководческим четырехколесным универсально-пропашным тракторам. Приведены конструктивные особенности устройства разрабатываемого переднего моста. Описано техническое решение, принятое в конструкции механизма поворота направляющих колес этого переднего моста. Приведены устройство и принцип работы механизма поворота направляющих колес и различные режимы его работы. Примененный на переднем мосте механизм поворота направляющих колес позволяют осуществлять две функции управления транспортом: поворот направляющих колес по традиционной схеме для движения в транспортно-рабочем режиме и поворот направляющих колес в противоположные направления для разворота на месте. Новшество, примененное на переднем мосте улучшает поворотливости направляющих колес и обеспечивает минимизации радиуса поворота трактора.

Keywords: tractor, front axle, wheel, frame, turning mechanism, agility, maneuverability, turning radius.

Ключевые слова: трактор, передний мост, колесо, остов, механизм поворота, поворотливость, проходимость, радиус поворота.

Introduction. In cotton-growing farms, despite a number of significant shortcomings, a three-wheeled tractor is used for inter-row cultivation of cotton crops. This is due to the good fit of the design of this tractor into the aisles with developed cotton bushes and high maneuverability achieved due to the minimum turning radius [1].

The disadvantages inherent in a three-wheeled tractor are to a certain extent absent in four-wheeled tractors with wheel arrangements 4K2 and 4K4. The use of these tractors in cotton growing helps to reduce the negative technogenic impact on the soil by reducing the total area covered by wheel tracks, reducing the pressure on the soil in the zone of the bearing area of the tractor wheels, more rational distribution of the masses of the machine-tractor unit along the axles and reducing wheel slip. However, the lack of agrotechnical clearance and the limited rotation limit their use in cotton growing [2].

Purpose of the study - research on the design of the front axle for the development of a high-clearance and highly maneuverable four-wheeled cotton-growing tractor.

Materials and methods. Currently, the vast majority of four-wheel tractors are equipped with two types of front axles [1-4], in one of them the front axle beam is located along the axis of rotation of the guide wheels (Fig. 1, a), and in the other - above the axis of rotation of the guide wheels (Fig. .1b).

Figure 1. Designs of front axles of wheeled tractors

In the first case, the agrotechnical patency of a four-wheeled tractor is regulated by reinstalling guide wheels with different radii. If it is necessary to increase the agrotechnical cross-country ability of a four-wheeled tractor, guide wheels with a large radius are installed, and in case of a decrease, on the contrary, with a smaller radius.

In the second case, an increase in the agrotechnical cross-country ability of a four-wheeled tractor can be achieved both with a change in the radius of the guide wheels, and without changing the radius of the guide wheels, but by increasing the length of the knee of the front axle.

Each of these front axles has its own advantages and disadvantages. Despite these advantages and disadvantages, both of them have a common disadvantage associated with the limited rotation of the guide wheels.

World experience in the creation of four-wheel tractors shows that with limited rotation of the guide wheels, it is difficult to achieve high maneuverability.

The limitation of the rotation of the guide wheels is due to the size of the wheels, the width of the frame, the presence of a spar in some tractors, as well as the gauge of the four-wheel tractor.

Particularly the most difficult issue remains the choice of the dimensions of the guide wheels, because they must meet compromise requirements. On the one hand, a high vertical load at low pressure on the soil requires the use of large guide wheels, and on the other hand, due to the conditions of fit into the aisles of cultivated crops and ensuring the maximum angle of rotation without touching the wheels on the frame of a four-wheel tractor, they must be small.

This problem has become especially acute after the widespread use of combined implements with a tool attachment in front of a four-wheel tractor and intensive technologies with a wide use of fertilizers, herbicides and pesticides. To ensure the carrying capacity of the front axle and meet the requirements for the pressure of the mover on the soil, they began to use guide wheels of a larger diameter. This entailed a change in the weight distribution along the tractor axles from 35/65% to 40/60%.

Although the increase in the diameter of the guide wheels led to a positive redistribution of mass along the axes of the tractor, it led to a deterioration in the angles of rotation of the guide wheels, and hence the turning radius of the tractors.

As a result, the minimum turning radius for most four-wheeled tractors is 4–5 m [5]. The best foreign four-wheel row-crop tractors turn the steering wheels only by 55 ° ... 65 ° (for example, New Holland tractors, etc.).

The agility of the guide wheels is of particular importance for four-wheel row-crop tractors used in the cultivation of cotton. Due to the existing kinematic and dynamic parameters of cotton machine-tractor units compiled on the basis of these tractors, a significant part (up to 5%) of the sown areas is alienated to the headlands, causing significant damage to the economy of producer farms in the conditions of self-supporting, rental and farms.

In order to reduce the size of headlands, research is being carried out to minimize the turning radius of wheeled tractors both in our country [1-2] and abroad [6, 7]. Among these works, from the point of view of increasing maneuverability and cross-country ability, the work carried out in the direction of minimizing the turning radius of the tractor and increasing the agrotechnical clearance under the front axle beam is of the greatest interest. 

Taking into account the emerging trend in improving the design of the front axles of wheeled tractors, “DTCAE LLC” began work on creating a high-clearance, highly maneuverable front axle for cotton-growing four-wheeled universal row-crop tractors.

Results and discussion.  When designing, the high-clearance, highly maneuverable front axle (Fig. 2), which is being developed at “DTCAE LLC”, was based on:

- forks 18 assembled with guide wheel 19;

- a mechanism for turning the guide wheels, which allows for two functions of transport control: turning the guide wheels according to the traditional scheme for movement in the transport and working mode, turning the guide wheels in opposite directions for turning on the spot;

- hydraulic differential turning mechanism designed to reduce the turning radius for turning on the spot of the 4K2 tractor without an active drive of the front axle;

- high-clearance version of the tractor - for cotton-growing applications, including for wide-cut and combined units.

Figure. 2. High clearance, highly maneuverable front axle for cotton-growing four-wheeled universal row-crop tractors

Taking into account the above, at the level of the patent [8], a front axle was developed, which is made in the form of a round beam 16 with pivots 2 of the pivot pin 1 at the ends and with the possibility of transverse rolling on the axis 15 of the front axle bracket 14 mounted on the front bar 13 of the tractor. Forks 18 with guide wheels 19 are installed along the axes of the kingpin.

The rotation of the guide wheels is carried out by a hydraulic actuator, which activates the turning mechanism of a functional type, operating in two modes: rotation of the guide wheels in the transport-working mode; turning the guide wheels when turning the tractor in place around the center of the rear axle.

The rotation of the guide wheels is carried out by two hydraulic cylinders of rotation 12 and 17, mounted on the front axle beam and connected through levers 3 and 11 with the shafts 1 of the swivel forks.

A feature of the turning mechanism is the design of the transverse link, which is made of two semi-links 4 and 10, made of pipes of different diameters. Moreover, the half-thrust pipe with a smaller diameter 10 enters the half-thrust pipe with a large diameter 4 with the possibility of moving these semi-thrusts relative to each other. The change in the length of the transverse link is carried out by two hydraulic cylinders 5 rigidly mounted on the semi-links of the transverse link. When the tractor is in the transport-working mode, the transverse link, therefore, the two half-links 4 and 10 are blocked into a single unit. Blocking is carried out by hydraulic locks 6 and 8 installed on hydraulic cylinders 5.

To bring the transverse link to the position corresponding to the transport and working mode of the tractor movement, the working fluid from the pump through the hydraulic distributor and through the hydraulic locks 6 and 8 enters the rod cavities of the hydraulic cylinders 5. Under the action of fluid pressure, the pistons of the hydraulic cylinders 5 retract the rods and move the half-rods 4 and 10 connected to the rods. At the same time, the rod cavities of the rotary hydraulic cylinders 17 and 12 are connected through a hydraulic distributor with a drain.

The amount of movement of semi-rods 4 and 10 is limited by the stroke length of the piston of hydraulic cylinders 5. After the pistons of hydraulic cylinders 5 have worked out their stroke, the half-rods 4 and 10 are blocked into a single whole thrust by hydraulic locks 6 and 8. The length of the blocked transverse link is equal to the sum of the displacements of the two semi-links, i.e. the sum of the stroke lengths of the hydraulic cylinder pistons. With this blocking of half-links 4 and 10, the turning mechanism works like a conventional steering linkage.

To improve the turn in the transport and working mode of the tractor and ensure a turn on the spot, a hydraulic differential turning mechanism (HDMP) has been developed, which ensures the rotation of the rear wheels in opposite directions and at different speeds.

To turn the universal row-crop tractor to the right, the driver-operator turns the steering wheel to the right and slows down the right rear wheel. At the same time, hydraulic cylinders 17 and 12 turn half-rods 4 and 10 by means of levers 3 and 11, and together remove the kingpin 2 of the steering wheel clockwise and the steering wheels turn to the right side, and the tractor turns around the braked right rear wheel.

Turning the tractor to the left is carried out in exactly the same sequence, but in the opposite direction with the left rear wheel braked.

When the tractor turns sharply in place with a minimum radius, the steering wheels turn in opposite directions. In this mode of operation, the steering mechanism does not work like a conventional steering linkage.

In the side turn mode, i.e. turning the tractor on the spot, the working fluid is fed through the distributor and hydraulic locks 6 and 8 into the piston cavities of the hydraulic cylinders 5. This opens the valves of the hydraulic locks 6 and 8. The rod cavities of the hydraulic cylinders 5 and the piston cavities of the hydraulic cylinders of rotation 17 and 12 are connected to the drain. As a result of this, the half-draughts are unlocked. Under the action of the pressure of the liquid entering the piston cavities of the hydraulic cylinders, the pistons extend the rods and push apart the half-rods 4 and 10 connected to them. Through the levers 3 and 11, half-rods 4 and 10 turn the pivots 2 mounted on them with forks 18 with guide wheels 19. The amount of movement of half rods 4 and 10 corresponds to the rotation of the guide wheels by 70° and is limited by the length of the piston stroke. In this case, the guide wheels turn in opposite directions.

In case of a sharp turn to the right, with the right rear wheel braked, half-rods 4 and 10 are unlocked by hydraulic locks 6 and 8. Due to the unlocking of the half-rods, the integrity of the steering linkage is violated, and the pistons, under the action of the pressure of the fluid entering the piston cavities of the hydraulic cylinders of rotation 17 and 12, extend the rods and push apart the half-rods 4 and 10 connected to them. Half rods 4 and 10 through the levers 3, 11 turn the kingpins 2 with forks mounted on them with guide wheels. As a result, the guide wheels turn in different directions so that the angles of deviation from the axis of symmetry of the tractor of the left guide wheel reach 70°, and the right guide wheel - up to 110°. In this case, the working fluid under pressure flows through one of the hydraulic lines to the spool mechanism. When the hydraulic motor is turned on by the handle of the tractor hydraulic distributor, the disengaged rear wheels, rotating in different directions, turn the tractor in place to the left or right, depending on which direction the hydraulic motor is switched. In this case, the tractor makes a sharp turn around the braked right or left rear wheel or in place around the center of the distance between the rear wheels with the parking brake applied and the rear wheels disengaged.

After turning the tractor on the spot, the driver-operator, by means of the hydraulic control system of the turning mechanism, brings the transverse link to the position corresponding to the transport and working mode of the tractor movement.

Conclusions and offers. Thus, the developed mechanism for turning the guide wheels allows for two functions of tractor control: rotation of the guide wheels in the traditional pattern for movement in the transport-working mode and rotation of the guide wheels in opposite directions for turning on the spot. The use of this mechanism in the construction of a four-wheeled cotton tractor improves the agility of its guide wheels and minimizes the turning radius.

References:

1. Akhmetov A.A. Front axles of universal row-cultivator cotton tractors. - Tashkent: Fan, 2014. - 146 p. (in Russian)
2. Akhmetov A.A. Universal row-crop tractors for inter-row cultivation of cotton crops. - Tashkent: Fan., 2017. - 240 p. (in Russian)
3. Parfenov A.P. Trends in the development of agricultural tractor designs // Tractors and agricultural machines, 2015. - No. 5. - P. 42–47. (in Russian)
4. Sharipov V.M. Design and calculation of tractors. - Moscow: Mashinostroenie, 2009. - 752 p. (in Russian)
5. Anilovich V.Ya., Vodolazhenko Yu.T. Design and calculation of agricultural tractors. - Moscow: Mashinostroenie, 1976. - 456 p. (in Russian)
6. Zeleny P.V., Shcherbakova O.K., Yatskevich V.V. On reducing the turning radius of an agricultural wheeled tractor // Innovation in science, industry and education. Sat. materials scientific and technical conference of young scientists. – Vitebsk, Belarus October 28 – 29, 2010. (in Russian)
7. New Holland Super Steer Tractor 716B. 76 Inch. TC35-TC45D. Operator's Manual_86608542. - rr. 24. (in Russian)
8. Patent UZ IAP 06073. Universal row-crop tractor / Akhmetov A.A., Usmanov I.I., Ruziev D., Akhmedov Sh.A. Rasmiy akhborotnoma. - 2019. - No. 12. (in Russian)