Algorithm for Selecting a Base Tractor Model to Form a Tractor Train

. The main quality indicators of tractor trains (the number of trailers and their total load capacity, speed and stability of movement, braking distance, etc.) depends largely on the correct choice of the type of a base tractor. The existing methodological principles for optimizing the dimension range of agricultural tractors do not take into account the type of trailers. Therefore, the task of a rational choice of the base tractor type, taking into account the most complete utilization of the capacity of existing trailers and engine power, has become rather relevant. ( Research purpose ) Selection of a tractor model for hitching a group of 2PTS-4-793-03A two-axle trailers according to the criteria for carrying capacity and energy consumption of a tractor train. ( Materials and methods ) The authors have studied mass, weight and velocity parameters of the 2PTS-4-793-03A two-axle trailers, as well as the parameters characterizing the mechanical capabilities of the studied tractor. The studies employed the methods of implement mounting on machine-tractor units and elements of the theory of a tractor. ( Results and discussion ) The authors o ﬀ er an algorithm of solving a problem of choosing a tractor. As a results, the ТТ Z 60.10 tractor with a wheel formula of 4 К 2 available at farm enterprises and included in machine-and-tractor ﬂ eets and clusters has been selected as a power base of a tractor train. The authors have determined the number of trailers, which equals four, the tractor train speed ranges of 4-28 kilometers per hour, the tractor engine power amounting to 8.5-59.5 kilowatts, changes in critical values of the e ﬀ ective engine power corresponding to 13.492-94.444 kilowatts, as well as speci ﬁ ed some other criteria. ( Conclusions ) The ТТ Z 60.10 tractor with a wheel formula 4 К 2 and 46.7 kilowatt of e ﬀ ective engine capacity has been considered the optimal choice. It has been proved that this tractor can move four 2PTS-4-793-03A two-axle trailers with a total weight of 15,600 kilograms along asphalt-concrete roads with a rational speed of 9.505 kilometers per hour. The rationality of choice has been proved by calculating energy saving criteria: full traction e ﬃ ciency accounts for 60 percent, engine load factor is 89 percent, and traction power utilization amounts to 96 percent.

(Результаты и обсуждение) Предложили алгоритм решения задачи по подбору модели трактора. В качестве энергетиче-M any qualitative indicators of tractor trains (the number of aggregated trailers and their total load capacity, speed and stability of movement, the length of the braking distance) are primarily determined by the traction and energy characteristics of the basic tractor [1]. Therefore, the rational choice of the type (model) of the basic tractor is important, taking into account the fullest use of its weight and power as part of the tractor train.
When completing energy-saving machine-tractor units it's necessary to perform three tasks [12]: -the first -to choose a machine for agricultural work in the unit with the known tractor; -the second -to choose a tractor to a known agricultural machine to perform a given technological operation; -the third -to determine the rational speed of the machine-tractor unit with its known composition.
These algorithms do not concern transport units. Nevertheless, the second option is quite suitable for the selection of the basic tractor to the known model of the tractor trailer after a small improvement.
RESEARCH PURPOSE is to choose a tractor model for aggregation with a group of 2-axle trailers 2PTS-4-793-03A and according to the criteria of load capacity and energy consumption of a tractor train.
MATERIALS AND METHODS. The initial constructional weight of the trailer m ПК = 1700 kg, the average weight of the load m Г = 2200 kg. The permissible maximum speed of the tractor with trailers is 28 km/h. It is assumed to use a tractor with the following characteristics [11,[13][14][15]: -wheel formula 4K2; -mechanical transmission efficiency η mp = 0.9; -permissible coefficient of slipping δ =18%; -coupling weight utilization factor λ=0.75; -coefficient of traction of tractor wheels with soil μ = 0.75; -coefficient of wheels rolling resistance on roads with asphalt concrete covering typical for a tractor train f = 0.018.
In the process of research, the basic provisions of the theory of the tractor and methods of acquisition of machinetractor units were used. RESULTS AND DISCUSSION. We take the following algorithm for solving the task.
1. At the first stage, as the energy base of a tractor train, it is advisable to choose a tractor TTZ 60.10 with a wheel formula 4K2, consisting of a balance of farms, machinetractor parks and clusters. The operating weight of this tractor m Т =3341 kg satisfies the condition m Т >2600 kg, then the maximum value of the hook force is determined by the formula: = 0.373 m Т g = 0.373⸳3341⸳9.81 = 12.225 kN [15]. 2. Next, we calculate the number of trailers n in the tractor train from the condition P кр ≤ , where P кр -the total resistance force of the group of trailers in the train: P кр = nG П (sinα + fcosα), kN [15], where G П = (m ПК + m Г )g -the weight of one trailer 2PTS-4-793-03А with a load, kN; α -the angle of longitudinal inclination of the support surface of the road.
where i -the slope of the road. If V min ÷V max = 4÷28 km/h and G П = 38.259 kN we have: kW.
5. The range of critical values of the tractor engine effective power: . (5) We substitute values and get: 9. The maximum power on the tractor hook is: , (6) or kW.
If P кр = 10.752 kN we'll get: Thus, V min (4 km/h) < V рац (9.505 km/h) < V max (28 km/h). 12. The power expended when moving a train at a speed of V рац : , That is kW.
13. The effective power of the tractor engine, spent on overcoming the traction resistance P кр at the speed of the train V рац , is equal to: . (10) If P кр = 10.752 kN and V рац = 9.505 km/h we'll get: kW.

CONCLUSIONS.
The ТТZ 60.10 tractor with a wheel formula 4К2 and 46.7 kW of effective engine capacity has been considered the optimal choice. It has been proved that this tractor can move four 2PTS-4-793-03A two-axle trailers with a total weight of 15.600 kg along asphalt-concrete roads with a rational speed of 9.505 km/h. The rationality of choice has been proved by calculating energy saving criteria: full traction efficiency accounts for 60%, engine load factor is 89 %, and traction power utilization amounts to 96%.