V.N. Perevoznikov, E.A. Osipov
At OJSC «Holding management company «Bobruiskagromash» three types of two-axle balancing bogies with four wheels—differing in track gauge and wheelbase—were previously used on tractor trailers and transport-technological machines for applying organic fertilizers with load capacities ranging from 7 to 15 tons. This variety led to issues with product identification both during manufacturing and operation by consumers.
Further research and development aimed at expanding the range of tractor trailers and semi-trailers with load capacities over 20 tons, based on standard two-axle balancing bogies with high-capacity tires, in practice resulted in overloading the tractor’s tow hitch device (Type of pitching device), causing impact loads, and poor longitudinal stability. These issues exacerbated negative operational phenomena.
The key point is that when developing tractor semi-trailers and semi-trailer agricultural transport and technological machines with a lifting capacity of more than 20 tons on a two-axle chassis of the balance bogie type with 4 wheels, it is structurally difficult to solve the problem of ensuring the longitudinal stability of the machine. The point is that in the case of a rearward displacement of the chassis in the direction of travel, in the loaded state, a load exceeding the permissible value is transferred to the TPD of the unit, and when the chassis is shifted forward, to reduce the load on the Type of pitching device, a negative load (upward) will be observed on the coupling loop of the tractor semi-trailer or semi-trailer agricultural transport and technological machine as it is unloaded, which is not allowed according to the safety requirements of the technical regulations of the Customs Union. As a consequence, with the appearance of a negative load on the coupling loop of machines with a shifting center of gravity during unloading, such as spreaders of solid organic fertilizers with a chain-slat bottom conveyor or semi-trailers with a movable front side, there is a decrease in the coupling mass of the tractor with a subsequent increase in its slippage in the field during the main work. One possible solution is a three-axle system of the "TRIDEM" type with six wheels, but this would require the addition of one or two axles with steerable wheels to prevent lateral skidding during turns, necessitating a complex design.
The designers at OJSC «Holding management company «Bobruiskagromash» led by E.A. Osipov, adopted the most rational approach by proposing a three-axle combined chassis system consisting of a rear balancing bogie with four wheels and a front single-axle trailer (see diagram). The rear balancing bogie is an in-house manufactured product, standardized for trailers and machines with load capacities over 14 tons, with minor modifications, ensuring high manufacturability and reliability.
Diagram – Vehicles with a three-axle combined chassis system:
a) Liquid Organic Fertilizer Application Machine (MJU-20A)
b) Tractor Semi-Trailer PST-24
c) Solid Organic Fertilizer Application Machine (MTU-24)
d) Special Semi-Trailer PS-60B
The front trailer unit is unified across all new and modernized three-axle transport-technological machines and tractor trailers of types such as MTU, MJU, PST-24, PS-60B, and always provides a positive vertical load on the tractor’s TPD in both loaded and unloaded states within the allowable limits (not less than 50 kg). Additionally, the trailer has a sprung axle, eliminating vertical impact loads on the tractor’s DCD and improving operator conditions. The use of the new chassis design with six wheels on tires 600/50-22.5, according to calculations, reduces the specific ground pressure by 30–35% compared to a four-wheel system on tires 700/50-22.5, enhancing field passability, especially on peatlands.
The novelty of this development is confirmed by Patent No. 4920 for Industrial Design "Three-Axle Chassis System," granted on the application dated 23.12.2021 (№ f20210242) and registered in the State Register of Industrial Designs on 15.04.2022.
In addition to all of the above, the chassis on 600/50-22.5 tires allows to reduce the height of trailers and semi-trailers by approximately 100 mm, which provides the possibility of increasing the volume of their bodies and lateral stability. Also, the width dimension, measured by tires, is 2.55 m versus 2.75 m, which corresponds to the traffic rules on public roads without special requirements.
Thus, for semi-trailers and semi-trailer vehicles with a load capacity of 14 to 18 tons and for 3-axle vehicles with a load capacity of 20 tons and above, a series of unified balance bogies on wheels with a landing diameter of 22.5" and tires 20.0/60-22.5 and 24.0/50-22.5 has been created, differing only in the width of the tires and wheels, as well as in the disk offset to obtain different tracks.
The developed chassis system has been implemented on new and serial products (PST-14, PST-18, PST-24, RU-8, MTU-11, MTU-15, MTU-18, etc.), enabling modernization of existing machines to eliminate deficiencies, increase load capacities and productivity, and improve passability through reduced ground pressure (e.g., MTU-20A, MTU-24A, MJU-20A, PS-45A, PS-60B, etc.).
For better possibility on low-bearing soils and, if necessary, to reduce ground pressure, the new four-wheel chassis system can also be installed on machines with load capacities from 8 to 12 tons.